# Replacing a thru-hull with a scoop strainer



## scboy (Dec 27, 2009)

I have searched the web, and asked a few folks, but I have not found any good info on substituting a scoop strainer for a mushroomhead thru-hull. I know that Maine Sail has done some good articles on replacing seacocks, thru-hulls, alternate backing plates, etc...., but it seems that no one has done much with scoops. 

The main purpose for my scoop is to provide positive pressure for the baitwell pump while running. I had also hoped that it might provide enough water through the baitwell pump to avoid having to run it while under way.

The picture below shows what is installed in the boat right now. I bought the boat this way and know that it is installed without a proper seacock. I do not want to install a seacock, but want to add a strainer scoop in lieu of the thru-hull with a reinforced flange on top of a backer plate. I perfer keeping the ball vavle that I have now for easy change out if it is needed at a later date.

(I tried posing a pic but my post count has to be two or greater.)

The biggest problem that I am trying to work out in my head, is how to install the reinforced flange after the scoop is attached to the hull. The scoop really does not allow for screwing it into the flange after the flange is mounted, since the scoop has to be facing towards the bow in the end. I'm afraid that if I try to screw it in the whole assembly will get tight when the scoop is not facing the bow.

OK everyone fire away. I hope I have explained the problem well enough.


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## scboy (Dec 27, 2009)

Building up my posts so I can post a picture


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## scboy (Dec 27, 2009)

Picture for the above post.


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## danielgoldberg (Feb 9, 2008)

I don't have an answer to your specific question (sorry), but this setup looks pretty scary. You don't have a valve on the through hull, so if that elbow fails for whatever reason (maybe someone stepping or dropping something on it) you have no way to close the hole. I'm not really sure why you don't want a true seacock, but the valve should go directly on the throughhull, and the elbow come after the valve, FWIW.


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## scboy (Dec 27, 2009)

I agree the setup is scary, that is why I started researching how to fix it. A flange adapter plate is like the sea **** without the valve. You add the ball valve to the top of it. It allows for change out of the ball valve if you need to without changing distrubing the thru-hull.

Maine Sail gave me the idea. See the below links.

Replacing Thru-Hulls and Seacocks Photo Gallery by Compass Marine at pbase.com

Seacock & Thru-Hull Primer/Pre Information Photo Gallery by Compass Marine at pbase.com


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## danielgoldberg (Feb 9, 2008)

I'm familiar with that product (and I actually have one on my boat). IMHO, they too are a compromise, albeit a lot better than just screwing a ball valve onto a through hull. 

But that said, now I think I understand a little better what you're thinking of doing. If you are determined to go that way, be sure to put the flange adaptor to the through hull, the ball valve to the flange adaptor, and then screw an elbow into the ball valve. In this application, however, I think you would be better off with a traditional seacock, and then just screw the elbow directly into the seacock. Less complicated, more robust, and it will not protrude as high. And if you use a true Marelon seacock and elbow, it will cost a lot less too, not to mention avoiding any concern about corrosion. Just one dope's opinion.


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## Maine Sail (Jan 6, 2003)

danielgoldberg said:


> I'm familiar with that product (and I actually have one on my boat). IMHO, they too are a compromise, albeit a lot better than just screwing a ball valve onto a through hull.


What do you consider a compromise about the flanged adapter? I have measured the wall thickness of many seacocks and the flanged adapter is as thick or thicker than most. I am helping a friend replace some Apollo seacocks that are about ten years old. They have zero corrosion yet the ball seats are done and opening and closing them is a bear even after trying to clean and lube them. Had a flanged adapter been used this replacement would have taken ten minues not ten hours and involved patching barrier coat etc. ect..



danielgoldberg said:


> If you are determined to go that way, be sure to put the flange adaptor to the through hull, the ball valve to the flange adaptor, and then screw an elbow into the ball valve. In this application, however, I think you would be better off with a traditional seacock, and then just screw the elbow directly into the seacock. Less complicated, more robust, and it will not protrude as high.


In this application I agree 100% with coming off the flange with the valve then elbow, but in many applications you simply do not have the height to do so and there are thousands of boats out there with elbows off the thru-hull. While certainly less than ideal it can work in a protected area of the vessel and there are many boats where you have no choice unless you want to re-locate a thru-hull. The OP clearly has the height and the ability to put the elbow after the seacock. This also looks like an open area that is not well protected and the lever arm of that set up becomes more dangerous when in an un-protected spot..



danielgoldberg said:


> And if you use a true Marelon seacock and elbow, it will cost a lot less too, not to mention avoiding any concern about corrosion. Just one dope's opinion.


I'll give you the corrosion piece but the price of Marelon is not less, at least where I shop..

3/4" Flanged adapter = $24.99
3/4" Groco valve = $18.80
TOTAL Flange/Valve = $43.79

3/4" Marelon Seacock = $44.91

3/4" Groco Flanged Seacock = $32.39

P.S. Marelon flanged seacocks are basically flanged adapters too. The flange is threaded into the bottom of the valve then kept from un-threading with a very small stainless pin..


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## scboy (Dec 27, 2009)

This boat is an Mako 191. It does not sit in the water. I do plan on taking this boat to the nearshore reefs and live bottom off the SC coast. The longest run will be 25 mi out. The hull will be pounded. Probably for no more water contact than it will see. I should just put an seacock on and be done with it. I still have the problem of getting the scoop strainer to the seacock though.

Picture of the scoop:

Groco Bronze Thru-Hull Scoop Strainers


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## Maine Sail (Jan 6, 2003)

scboy said:


> This boat is an Mako 191. It does not sit in the water. I do plan on taking this boat to the nearshore reefs and live bottom off the SC coast. The longest run will be 25 mi out. The hull will be pounded. Probably for no more water contact than it will see. I should just put an seacock on and be done with it. I still have the problem of getting the scoop strainer to the seacock though.
> 
> Picture of the scoop:
> 
> Groco Bronze Thru-Hull Scoop Strainers


A scoop is no different than a thru-hull and either can be threaded into a flanged seacock or a flanged adapter and with either you'll still need to cut them to insert length. On a sail boat you'd want the strainer facing aft but on CC, for what you'd want to do, you'll want it facing forward. If you can thread it in tight enough, and get it to align properly you can sometimes avoid the hull screws.

Be sure this scoop won't be out of the water on plane and that it is close enough aft to not leave the water when planing..


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## danielgoldberg (Feb 9, 2008)

Hey there MS. You certainly are more knowledgeable about this stuff than am I, but since you asked ...

It's a compromise not because the specific piece of hardware isn't first rate, which it is. But you still are threading a ball valve into the flange adaptor, and that presents another potential failure point. It's easier to snap off the ball valve, there's more of a chance the connection will leak, etc. You are right that if you need to replace the valve it's easier to change just a ball valve, but a properly installed, properly maintained, quality seacock is not going to fail with anything close to regularity, if ever. Moreover, you don't absolutely need to through bolt the seacock through the hull. You could laminate in either a resin soaked piece of ply, maybe G10 or something comparable, and bolt to that alone.

As to your second point about not having enough room to put the ball valve onto the flange adapter and the elbow after that, isn't that an argument for using a true seacock? If you have enough room for the flange adapter, you most likely have enough room for a seacock, no?

In terms of pricing, at least at West and Defender, the Marelon units uniformly are less expensive than the bronze seacocks. And at the larger sizes (an inch or more), the bronze are substantially more expensive. Seems you found a serious sale at Hamilton re: the bronze seacock. I wasn't comparing to the flange adapter with ball valve, but your numbers bring them within pennies anyway.

I didn't know that about the Marelons re: the pin! Learn something new every day I guess.

Hope you and your family had a good holiday!


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## scboy (Dec 27, 2009)

This area where the thru-hull is located is protected. I have the main deck plate pulled right now to gain access. when the deck plate is in there are only two 10" round pop out plates to access the bilge.

Maine Sail,if I put in one of the Perko or Groco all in one Strainer Scoops do I really need a flange adapter plate or a true seacock? I noticed that the scoop has holes for bolts thru the strainer housing? Also if I put bolts in the strainer housing to mount it to the hull, does it matter if I use stainless in lieu of bronze, if the boat is trailered?

Another picture showing where the deck plate fits:


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## danielgoldberg (Feb 9, 2008)

I know you asked MS, but to me, from the pictures you've posted and the work you're talking about doing anyway just to get the scoop in, I don't see the benefit of not using a seacock, unless you really need/want to save the few bucks on the hardware (and if that's the case, then you could go with a Marelon seacock and be at the same price point).

By the way, if you are keeping the boat on a trailer and not in the water, the corrosion benefit of Marelon really doesn't come into play.


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## scboy (Dec 27, 2009)

Thanks Dan for responding. I always listen to everyone's opinions, and try to educate myself before going off halfcocked. I want to do this right, but I do not want to overkill it either. Fiberglass is not my thing. Metal and wood working are, so I am going to educate myself about fiberglass. LOL I have learned more about seacocks in the last week than I really wanted to, but that is what owning a boat is about. At least it is for me.


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## Maine Sail (Jan 6, 2003)

danielgoldberg said:


> It's a compromise not because the specific piece of hardware isn't first rate, which it is. But you still are threading a ball valve into the flange adaptor, and that presents another potential failure point.


If the pieces are as thick and robust as the bottom side of a cast bronze seacock then it is going to be as tough. NPT to NPT fittings are very, very robust and the flanged adapter meets the ABYC standards of 500 pounds static load just as an Apollo or Groco or Spartan cast bronze seacock would. Again, I have measured the cross sectional thicknesses of many seacocks and the flanged adapter and ball valve combination are as thick and in some cases thicker and stronger.



danielgoldberg said:


> It's easier to snap off the ball valve,


What are you basing this statement on? My micrometer and calipers are in awe that this could happen "easier"?



danielgoldberg said:


> there's more of a chance the connection will leak, etc.


If installed correctly and with the right pipe dope I have yet to see one leak. I used to work in the hydronics industry and have seen NPT / NPT fittings with pipe dope carry over 1000 PSI. You are dealing with single digit PSI on a seacock. Even with one more properly matching threaded fitting you are still in far better hands than the thousands of boats with mismatched threads NPS/NPT that are out there.. (NPT = tapered threads / NPS = straight threads)

A properly matched thread on the right NPT/NPT and an improperly matched thread NPS/NPT like the elbow on that thru-hull in the OP's photo:











danielgoldberg said:


> You are right that if you need to replace the valve it's easier to change just a ball valve, but a properly installed, properly maintained, quality seacock is not going to fail with anything close to regularity, if ever.


As someone who worked in boat yards in my younger days and was small enough to be deemed the seacock grunt, stuffing box grunt and rudder box grunt, alignment grunt, bilge grunt etc., and who has replaced hundreds of seacocks, of all types, from tapered cones to Marelon to bronze and stainless ball types I am having a tough time understanding where you came up with this idea?

The boat I am currently helping out on had these valves installed about 10-11 years ago and the owner is fastidious and closes them and cycles them every time he is on and off the boat. I have had numerous Marelon valves / handles fail me, three on my own vessel, which I know was properly maintained. This one was not even being used as a seacock..









These valves are getting replaced this spring because they're getting near impossible to close. They are about 8 years old and have been well maintained and exhibit no signs of corrosion. I suspect the ball got buggered up with some marine growth and it scored the valve seats and is causing the binding sadly no flanged adapter:











danielgoldberg said:


> Moreover, you don't absolutely need to through bolt the seacock through the hull. You could laminate in either a resin soaked piece of ply, maybe G10 or something comparable, and bolt to that alone.


No you don't but if you are that worried about the strength of a flanged adapter / ball vale I am surprised you'd suggest anything other than through bolting?

Try this on for size. Install a flanged seacock with no thru-hull into a solid fiberglass backer. A number of builders do this to keep a smooth & fast hull, they then barrier coat the inside of the hull hole and thru-bolt and seal the seacock and it's flange to the hull. This makes for a nice neat install and a fast bottom. How would you feel about screwing the seacock in without thru-bolts in this type of application? I think it can be done but I would personally thru-bolt.

I also show a very strong method and way of avoiding thru-bolting on my web site.



















danielgoldberg said:


> As to your second point about not having enough room to put the ball valve onto the flange adapter and the elbow after that, isn't that an argument for using a true seacock? If you have enough room for the flange adapter, you most likely have enough room for a seacock, no?


No, not in all situations like the one below. There are no commercially available flanged seacocks that could fit in this area height wise. This is a separate and protected compartment that has a teak cover with bungee. I had to either use a flanged adapter or a thru-hull with a valve like the OP has. The flanged adapter is multiples stronger and properly matches the threads. This fit was so tight that I had to bend the handle down some. 









I actually installed this set up on my shop bench, inserted an 8" nipple into the end of the valve and stood on it. All it did was flex my work bench. In that location it will never see even close to 200 pounds at the end of an 8" lever. Some situations on some boats don't always fit the stereo typical ideal installation..



danielgoldberg said:


> In terms of pricing, at least at West and Defender, the Marelon units uniformly are less expensive than the bronze seacocks. And at the larger sizes (an inch or more), the bronze are substantially more expensive. Seems you found a serious sale at Hamilton re: the bronze seacock. I wasn't comparing to the flange adapter with ball valve, but your numbers bring them within pennies anyway.


I don't take anything at WM seriously, especially the prices, and I am a Port Supply customer.. As for Defender I don't usually think of them for seacocks as I usually buy that stuff from Hamilton because they have perhaps the largest in-stock selection. Those are not sale prices but the regular Hamilton Prices..

Defender
Apollo Bronze 1 1/2" Flanged Seacock = $94.99

Marelon 1 1/2" Flanged Seacock = $97.40

Still fairly comparable even in 1 1/2"



danielgoldberg said:


> I didn't know that about the Marelons re: the pin! Learn something new every day I guess.


Interestingly enough the Marelon seacocks are in-fact constructed very similarly to a flanged adapter and a valve..



danielgoldberg said:


> Hope you and your family had a good holiday!


We did!! You too!


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## danielgoldberg (Feb 9, 2008)

Maine Sail said:


> Interestingly enough the Marelon seacocks are in-fact constructed very similarly to a flanged adapter and a valve..


A ha!!!!!!! So you admit I'm right and that Marelon seacocks are every bit as good as your flange adaptor setup! 

Joking aside, as I mentioned at the outset, you clearly are more knowledgeable on this stuff than me. But that said, it still seems to me that having one less connection is better, everything else being equal. Likewise, it strikes me that having the valve sit that much more proud on top of the flange adaptor and being screwed on like that must be easier to break than a flanged seacock alone. I certainly could be wrong here, but I bet that if you were to swing a sledgehammer at a ball valve sitting on top of a flange adaptor, you would have a better chance of breaking the setup as compared to swinging a sledgehammer at a flanged seacock. I certainly could be wrong about that (but I'll never admit it).

By the way, and just so it's clear, I'm not criticizing the flange adaptor setup or claiming that it's improper. Indeed, based on your say-so we installed one on one of our through hulls. All I'm suggesting is that, all else being equal, it seems a true flanged seacock is likely a better way to go. I take it you disagree with that, and you clearly have more direct experience than do I.

On the point about clearence for putting in an elbow, I take your point that there could be an installation requiring that compromise, but short of that you certainly agree the valve should go directly on the through hull, no?

I see your links about pricing, but when I jump on to Defender's/West's website, I still get numbers that are more disparate than what you are showing in your links. Who knows.


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## Maine Sail (Jan 6, 2003)

danielgoldberg said:


> On the point about clearence for putting in an elbow, I take your point that there could be an installation requiring that compromise, but short of that you certainly agree the valve should go directly on the through hull, no?


Yes I agree 150% with that. My only point is that you can't always do that in every situation. If I could have done that, even if it meant giving up the flanged adapter, I would have..


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## GaryHLucas (Mar 24, 2008)

I find these plumbing threads interesting. I design and build membrane systems working from 5 psi to 1200 psi. We use all kinds of valves, and lots of actuated valves, some that open and close 100,000 times per year.

I love it when people say "Don't use a ball valve, use a seacock!" Hey, that Marelon seacock IS a ball valve with a flanged adapter! The old time seacocks that were cast in one piece with the flange, they were tapered plug valves. It was bronze to bronze so they needed lubrication, and adjustment of the nut holding the plug in. Sometimes you needed to lap the plug into the body with lapping compound to get them to seal again.

Seriously, have any of you EVER seen a metal elbow fail? Have you EVER seen one actually broken? What EXACTLY is that valve/seacock protecting you from? How many boats sink from a failed seacock/valve? If you can't close the valve because it is frozen, does your boat sink? If an all bronze seacock is good why is an all bronze gate valve with metal to metal seating bad?

Isn't the weak link in all this actually the hose, and hose clamps attached to the valve/seacock? If whatever valves/seacocks you have are PROPERLY installed, and MAINTAINED, are you any less safe?

My experience with ball valves is that these are just about one of the best possible designs for a valve, bar none. Thats because they naturally seal BETTER as the seats wear, where most other types of valve seal worse as they wear. Plus the ball is self-aligning in teflon seats, they almost never sieze up, unless the something has attached itself really well to the ball surface when they are CLOSED, not open! The weak point on most ball valves is the stem seal. It is also the weak point on virtually all other types of valves.

Ball valves 101:
Did you know that ball valves for high pressure MUST have leakage around the seal on the upstream side? If they can't leak by, the pressure forces the seal into the opening of the ball on any closed valve. Then they can't be opened and won't ever close again. I just forced a manufacturer to field rebuild 28 two inch stainless ball valves TWICE because they didn't get this right!


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## Maine Sail (Jan 6, 2003)

GaryHLucas said:


> I love it when people say "Don't use a ball valve, use a seacock!" Hey, that Marelon seacock IS a ball valve with a flanged adapter!


True and a ball valve threaded onto a thru-hull technically becomes a seacock though not a flanged seacock. One should use bronze or stainless UL Marine rated ball valves however as the Home Center valves are generally high zinc yellow brass..



GaryHLucas said:


> The old time seacocks that were cast in one piece with the flange, they were tapered plug valves. It was bronze to bronze so they needed lubrication, and adjustment of the nut holding the plug in. Sometimes you needed to lap the plug into the body with lapping compound to get them to seal again.


Not necessarily old time Spartan still makes tapered cone seacocks. If I had $20.00 for every one I've cleaned and re-built or had to lap fit over the years I'd have a Hinckley by now.. The big problem with them is the yearly maintenance and obviously the cost. That being said I have never seen a seacock out last either a Blakes or Spartan seacock. I have seen some tapered cone seacocks pushing 35 years and still going..

Spartan Tapered Cone Seacock











GaryHLucas said:


> Seriously, have any of you EVER seen a metal elbow fail?


Elbow no but thru-hull yes.



GaryHLucas said:


> Have you EVER seen one actually broken?


Never broken an elbow but I have seen seacocks fail and thru-hulls that have snapped.



GaryHLucas said:


> What EXACTLY is that valve/seacock protecting you from?


Water ingress. It needs to be able to open and close.



GaryHLucas said:


> How many boats sink from a failed seacock/valve?


According to one Boat US article 50% of the at the dock sinkings occur from underwater fittings. The vast majority are from stufing boxes then hose clamps but two of the failures in the article were directly attributed to gate valve failures. My interest in seacock safety began about 14 years ago when a spare alternator slid across a locker and hit my galley sink drain in rough seas. It cracked, but did not sheer, the thru-hull fitting and it began leaking badly. This was a valve on a thru-hull set up and not a properly flanged seacock. My boat was hauled and every seacock and thru-hull replaced with flanged seacocks. It scared the bejesus out of me..

Sub standard parts do fail:









Here's a direct quote from the article:

Boat US: 
_"Seacocks are widely regarded as being more reliable than gate valves. In an emergency, a quick glance at a seacock will tell you whether it is open or closed. With a gate valve, you can't tell. Gate vales also have a reputation for failing internally because the different metals-steel inside, bronze outside-aren't compatible. One of the sinking claims occurred when a bronze gate valve disintegrated and broke in two."_



GaryHLucas said:


> If you can't close the valve because it is frozen, does your boat sink?


If your seacock is frozen it is likely you have neglected the hoses and clamps too so I guess it could...



GaryHLucas said:


> If an all bronze seacock is good why is an all bronze gate valve with metal to metal seating bad?


For a few reasons. In industrial use the gate valve does not generally have barnicles trying to live in the seats preventing full closure and sealing. The gate valve is not of the type that can be looked at and determined to be open or closed (1/4 turn). I suspect that a properly built 85-5-5-5 bronze gate valve could survive as long as any other, despite the gate seat crudding up, but most are not and were not properly built as UL and ABYC will not approve them for this use, so why would Conbraco or Red White or Watts build to that standard?



GaryHLucas said:


> Isn't the weak link in all this actually the hose, and hose clamps attached to the valve/seacock?


Absolutely! I have seen far more hose and hose clamp failures than seacock failures but I have seen my fair share of seacocks so close to sinking a boat it is a wonder it survived. The use of improper hose for below water applications and cheap hose clamps is a huge pet peeve of mine. I have seen more cracked clear PVC hose than I care to admit as it gets brittle with time..



GaryHLucas said:


> If whatever valves/seacocks you have are PROPERLY installed, and MAINTAINED, are you any less safe?


If an owner takes the time to install the seacocks "PROPERLY", with a flange, using marine rated bronze or Marelon and keeping all metals the same grade it is also likely they replace their hoses & clamps on a regular basis too so I would guess that an owner with proper seacocks is likely to be more safe than the owner with PVC below the waterline and a mis-mash of metal soup.



GaryHLucas said:


> My experience with ball valves is that these are just about one of the best possible designs for a valve, bar none. Thats because they naturally seal BETTER as the seats wear, where most other types of valve seal worse as they wear. Plus the ball is self-aligning in teflon seats, they almost never sieze up, unless the something has attached itself really well to the ball surface when they are CLOSED, not open! The weak point on most ball valves is the stem seal. It is also the weak point on virtually all other types of valves.


I agree and as someone who once worked for a valve manufacturer I have seen some very long lived ball valves. The cavaet is the marine environment. I have seen far more ball types, Marelon, stainless and bronze toasted by growth etc. than I have tapered cone because they can not be rebuilt easily.



GaryHLucas said:


> Ball valves 101:
> Did you know that ball valves for high pressure MUST have leakage around the seal on the upstream side? If they can't leak by, the pressure forces the seal into the opening of the ball on any closed valve. Then they can't be opened and won't ever close again. I just forced a manufacturer to field rebuild 28 two inch stainless ball valves TWICE because they didn't get this right!


Don't some larger HP ball valves have internal by-passes to achive this too.?


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## GaryHLucas (Mar 24, 2008)

Maine Sail;554951Don't some larger HP ball valves have internal by-passes to achive this too.?[/QUOTE said:


> There are three simple ways that the bypass is done. One is to simply make the seals smaller in diameter than the opening in the body so water can flow around it. The downstream seal does all the work, the pressure pushes the ball against it. The second way is to cut notches around the edge for the water to pass through, or you can drill some small holes in between the ball and the seal.
> 
> Incredibly I got a whole shipment of valves without any bypass! From two different major manufacturers, supplied by different vendors! The second one sent out somebody to rebuild all the valves, and they did the same thing again! Fortunately I don't trust them to do it right, and inspected them myself.
> 
> ...


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## Maine Sail (Jan 6, 2003)

GaryHLucas said:


> Of course I own an Etap so I don't have as much skin in the game! On the Etap user forum everyone questioned WHY anyone wants a bilge pump? What's wrong with a bucket and a sponge?


Yep as a kid I had a 13 foot Whaler. Of course at 12-14 years old we loved to wave jump her. The cool thing was you could punch her right though a wave, not over it, and take it in the chest, yet hit the throttle and nearly all the water would simply roll out the stern because of the inherent buoyancy of the hull. That little boat took some abuse but never sank! If you're older than 16 don't wave jump a 13 foot Whaler unless you want your kidneys in your neck.. Those things land hard! Kids.....


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