# Fixed vs folding prop



## Greyhound37

Any guess as to the speed advantage of a 37' boat with a saildrive fixed vs folding prop. The fixed blades have a surface area of 35-38".(each blade is 7" x 3" +/-) What do you think, reaching 12 knots of wind... Fixed is 6.7knots on the polars.


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## msmith10

Not a simple question and as far as I know there's no simple answer or formula. Folding prop will be faster, that's about all you can say. 2-blade, 3-blade? Wind speed?
At hull speed it won't make any difference. In light air it will. If you spend most of your time racing, you'll want the folder, but then again if you race a lot you probably have one already. If you race occasionally but have to motor 3 miles up a river against 4 knot current to get back home, you may just decide to eat the speed loss. If you'd prefer to motor than sail when the weather gets rough, go with the fixed blade.
If I recall, PHRF gives you 8 seconds per mile for a 2 blade folder over fixed, 12 seconds for a 3 blade. It will cost you more than that, otherwise every racer would have a fixed prop.
If I had the money for a saildrive, though, I'd definitely spring for a feathering prop (slightly more drag than folding but better performance).


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## sailingfool

Half a knot.


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## msmith10

I was wrong. There is a simple answer, as good as any.


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## Greyhound37

8 seconds per mile or .5 knot, either way that is plenty. I was trying to decide if i want to replace the fixed prop now and guess i better.


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## msmith10

After replacing my 2 blade fixed with a folder several years ago, I went from 2nd-3rd place finishes to consistent 1st-2nd place in our club races. The folder doesn't back well, and it doesn't drive well in a chop, but I'd rather sail with rough seas anyway. It was worth the sacrificed performance under motor.


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## Greyhound37

Wow that is impressive. The Flexofold has cruising folding blades or racing using the same hub. I noticed that is the prop on several boats hauled near my boat Mumm 36, J-111
After spray applying VC offshore, would not be practical to be dragging a bucket under the boat. I hope to do 4 races this year but mostly cruise (as fast as i can go)
Thanks for the input!


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## Faster

We recently switched from a 2 blade fixed to a 3 blade Max prop.. the difference is remarkable and percentage wise much higher in the light air 3-4 knot boatspeed range than the powered up 5-6+ knot range. We probably reach our optimum upwind speed now in 5 knots less wind than before, and can ghost along at 3-4 knots where 2-3 would have been it before.

The feathering props do away with the folders' reverse issues, and 3 blades is much less vibration under power too... but at a cost, of course ($$$)


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## HUGOSALT

Simple answer of 1/2 knot seems about my experience with my 
Flex o Fold, but as stated above by Faster equal advantage is 
sailing in light conditions. 
Have cruising blades attached to saildrive very good forward speed
and no apologies for reverse, can and have stopped on a dime.
If you go flex-o-fold make sure you or your installer, properly
installs "tab washer" (simple but important). 
Also I used red loctite on my install, I will have to heat things up to remove, but hopefully will not be telling any stories about the 
time I lost my $1000+ prop in the middle of nowhere.


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## blt2ski

If racing, the credit of 9 or 15 secs locally for a 2 vs a 3 blade prop is NOT any advantage, you lose more than that, and gain way more speed with a folding/fixed prop than the credit is worth. .5-.75 additional speed seems to be the norm in speed gain. As faster said, you hit X knots in less wind etc etc.

Marty


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## chrism33

Slightly off topic.
When sailing, I been told to always keep the stopped engine in gear (forward or reverese) so the prop folds back quickly.

This doesn't seem right to me. 
Has anyone else heard this?


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## ltgoshen

My 1981 C&C 30 MK1 manual says 6.7 kt at 3400 rpms.
Well here is the thing the last owner put a folding prop on because he raced. I here a thud when I engage the prop. It don't back up very good. And I can only get around 2,000 rpms? If I push past that very long it starts wanting to smoke black smoke? Like ,I may be pushing too hard on the engine. any advice?








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## Faster

chrism33 said:


> Slightly off topic.
> When sailing, I been told to always keep the stopped engine in gear (forward or reverese) so the prop folds back quickly.
> 
> This doesn't seem right to me.
> Has anyone else heard this?


Check your transmission manual.. most do say to put in reverse while sailing, some do not, incl Yanmar, and suggest you leave it in neutral. Hurth says not to let the prop freewheel while in forward gear..

Either way, stopping the shaft will promote faster folding.. sometimes an unfolded prop will continue to spin otherwise... same with feathering. If your transmission advises against leaving the gear in reverse, you can always just do it long enough to promote folding and then leave it in neutral afterwards.



ltgoshen said:


> My 1981 C&C 30 MK1 manual says 6.7 kt at 3400 rpms.
> Well here is the thing the last owner put a folding prop on because he raced. I here a thud when I engage the prop. It don't back up very good. And I can only get around 2,000 rpms? If I push past that very long it starts wanting to smoke black smoke? Like ,I may be pushing too hard on the engine. any advice?


Sounds like you're overpitched.. a prop shop may be able to fix that for you and repitch your existing prop. btw that style of prop can sometimes only spin one blade open, causing a lot of vibration. If you find that happening get into the habit of giving things a quick spin in reverse prior to shifting to fwd.. seems to help. This mostly occurs when the prop comes to rest with the blades on a vertical axis, and one blade drops open due to gravity and lack of boat speed. The other blade, sitting in line with the shaft sometimes won't flip open leaving you with effectively a one blade prop - a very unbalanced circumstance!

The poor reverse performance is one of the costs of the reduced drag.. if you're not racing and want to avoid all this the Campbell Sailor prop is a good, relatively inexpensive option.


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## sailingfool

The opening thud is a characteristic of the folding prop. So is the poor reverse performance.

Another thing to check in terms of cruising RPMs is whether the tach is accurate. In-accurate tachs are pretty common, being off by a lot is not unusual. See

http://www.sailnet.com/forums/gear-maintenance/38029-diesel-rpm.html


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## SchockT

ltgoshen said:


> My 1981 C&C 30 MK1 manual says 6.7 kt at 3400 rpms.
> Well here is the thing the last owner put a folding prop on because he raced. I here a thud when I engage the prop. It don't back up very good. And I can only get around 2,000 rpms? If I push past that very long it starts wanting to smoke black smoke? Like ,I may be pushing too hard on the engine. any advice?


It looks like you have a Martec prop, which is the worst of the folders. I had one of those on my boat, until I found a good deal on a used Gori prop, which is the same idea except there are gears so the blades open and close together. It is definitely smoother, and reverse is much improved; still not great, but better than the Martec. It definitely sounds like the prop isn't sized correctly for your engine.


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## dacap06

SchockT,

Low RPM in gear and black smoke at speed? This description is the classic one for a prop that has too much bite for the motor driving it.


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## SchockT

dacap06 said:


> SchockT,
> 
> Low RPM in gear and black smoke at speed? This description is the classic one for a prop that has too much bite for the motor driving it.


 ergo the prop is not sized correctly (I guess I should have said "matched"?)

Whether the diameter is to big or the pitch is too great, the symptoms will be the same will they not?

Sheesh! A guy sure has to choose his words carefully on this site!


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## Stumble

Even for cruising there is no question that a folding or feathering prop is a massive increase in speed while sailing. Probably the single best thing you can do to increase the performance of a boat.

Yachting Monthly did a really nice right up of a number of different folding/feathering props, and what they found was pretty surprising. 
1) the drag from a fixed prop is roughly the same as HALF the drag from the entire rest of the boat.
2) backing characteristics of the good folding/feathering props was actually better than that for a fixed three bladed prop
3) feathering/folding props has less prop walk than a fixed generally
4) forward thrust from the feathering/folding props was within 5% of a fixed prop.

Based on this study I actually just replaced my fixed with an auto stream, and couldn't be happier. I wanted the flex-o-fold but couldn't find a US distributor. The results have been exacally what I expected. Similar forward speed and control, much better control in revers with less prop walk, and greatly increased speed while sailing.

A reprint of the study http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf


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## Chris.Carney

I'm on my 4th boat. This is the first one with a fixed prop. 2 blade. It's by far the slowest under power of any of my boats. (all yamaha all 30 or 31 feet) 

The boat moves under sail like it was coated in Vaseline so I can't gauge how the fixed props slows me down. 

I do catch a lot of seaweed under sail in seaweed season of spring (I sail Taiwan and the southern Japan islands) Good thing is that you don't need a waterproof lamp at night because the phosphorescence with every strike of the knife lights everything up.


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## sony2000

ltgoshen, you may have a 1to1 transmission and not a 2to1.
I suggest you go to the Moyer Marine forum to get the proper pitch numbers for C&C Mark1.
There is an active contributor from Halifax, with the same boat.


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## paul323

Recently replaced my fixed 3-blade with a Max-Prop (feathering).
Faster summed it up well in his post; as a datapoint for my 32 footer:

- 0.75 knot increase in speed under power. 
- Under sail is more difficult to quantify, but at least .5knots
- Improved backing up (yes, improved); less propwalk
- Light wind ability significantly improved

If you can afford it, the Max-prop is a quality piece of engineering, with many years of experience and success. And they are nice folks to deal with.


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