Changing propeller pitch

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eddystone

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A couple of years ago I had a Beta 30 fitted to my Sadler 32. Probably 25 would have been optimum but that needs an alternator upgrade which more or less wipes out the small price difference and others who had the same engine fitted to same boat recommended it over the 25. The 2 blade 15x12 fixed prop was replaced with a Featherstream 16x10.5. That's a pretty fine pitch and the reason was so that the engine could reach maximum or near revs (3600) at full throttle. No problems so far but last week was probably the first time I'd motored into a steep sea head to wind and progress was predictably slow, I mean 1.5 to 3 knots at 2500 revs (Actually it was completely stupid I could have made similar time reefed down with maybe 3 long tacks but that's another issue). The Sadler has a short WL so probably pitches more than modern boat of same OL and indeed it sounded like propeller was scrabbling for grip much of the time. Another pertinent fact is that I'm sure the prop is quite significantly fouled - it didn't move off the mooring from mid-March to early August. Notwithstanding that I wondered if I should change the pitch to get more grip - changeable pitch is one advantage of the Featherstream. Darglow says the next increment would result in max throttle achieving 3200 instead of 3600 rpm. I rarely use more than 3000 - is there a downside to this?
 
eddystone said:
A couple of years ago I had a Beta 30 fitted to my Sadler 32. Probably 25 would have been optimum but that needs an alternator upgrade which more or less wipes out the small price difference and others who had the same engine fitted to same boat recommended it over the 25. The 2 blade 15x12 fixed prop was replaced with a Featherstream 16x10.5. That's a pretty fine pitch and the reason was so that the engine could reach maximum or near revs (3600) at full throttle. No problems so far but last week was probably the first time I'd motored into a steep sea head to wind and progress was predictably slow, I mean 1.5 to 3 knots at 2500 revs (Actually it was completely stupid I could have made similar time reefed down with maybe 3 long tacks but that's another issue). The Sadler has a short WL so probably pitches more than modern boat of same OL and indeed it sounded like propeller was scrabbling for grip much of the time. Another pertinent fact is that I'm sure the prop is quite significantly fouled - it didn't move off the mooring from mid-March to early August. Notwithstanding that I wondered if I should change the pitch to get more grip - changeable pitch is one advantage of the Featherstream. Darglow says the next increment would result in max throttle achieving 3200 instead of 3600 rpm. I rarely use more than 3000 - is there a downside to this?
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Unless you have no choice heading directly into that sort of sea is a no brainier in my opinion far better to use a small jib and a combination of engine and sail and will be far less stress on boat and crew
 
eddystone said:
A couple of years ago I had a Beta 30 fitted to my Sadler 32. Probably 25 would have been optimum but that needs an alternator upgrade which more or less wipes out the small price difference and others who had the same engine fitted to same boat recommended it over the 25. The 2 blade 15x12 fixed prop was replaced with a Featherstream 16x10.5. That's a pretty fine pitch and the reason was so that the engine could reach maximum or near revs (3600) at full throttle. No problems so far but last week was probably the first time I'd motored into a steep sea head to wind and progress was predictably slow, I mean 1.5 to 3 knots at 2500 revs (Actually it was completely stupid I could have made similar time reefed down with maybe 3 long tacks but that's another issue). The Sadler has a short WL so probably pitches more than modern boat of same OL and indeed it sounded like propeller was scrabbling for grip much of the time. Another pertinent fact is that I'm sure the prop is quite significantly fouled - it didn't move off the mooring from mid-March to early August. Notwithstanding that I wondered if I should change the pitch to get more grip - changeable pitch is one advantage of the Featherstream. Darglow says the next increment would result in max throttle achieving 3200 instead of 3600 rpm. I rarely use more than 3000 - is there a downside to this?
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A fouled prop is such a big variable that I think your recent experience motoring into a steep sea shouldn't be used as evidence for a change. Moderate fouling of prop and hull takes two knots off our speed motoring.

I get very little hobby-horsing on our 32 and take some care to avoid excessive weight at the bow and stern. If the power is reduced through fouling then hobby-horsing will be greater in chop exactly for that reason.

Motorsailing through steep chop with mainsail alone always seems the best compromise to get somewhere fastest. Higher pointing and less heel than with sailing alone and with a VMG better than with either sailing or motoring alone.
 
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I am not a mechanic so my answer will be purely based on my experience. On my last boat a change of a gear box with different ratio (2,05:1. vs original 2,35:1)and a change of prop from 2-blade 16x11 to 3-blade 16x9 resulted in being over prop . Engine was a Volvo md 2030 with maximum rpm 3500 but with the new combination the engine could only achieve 3050-3100. The answer I got from mechanics and volvo dealers was that as long as I don’t run the engine at max for a long time (but do run it at high rpm occasionally), since it was a non turbo engine I wouldn’t face any problems. Next 6-7 years until selling the boat the engine was still running like a champ (after 3000+ hours) and all this time I noticed the following: The engine at 2200 rpm which was my new cruising rpm was giving the same speed like the “original“ cruising rpm 2500, consumption was the same or slightly less and of course the noise was much less. No smoke, no carbon built in the mixing elbow and in general I didn’t have any problems.
Of course the new setup was superb for motoring (but a pain for sailing) in comparison to the old but this was due to the extra 3rd blade! In any case you have a feathering propeller, so at least you can experiment.
 
scottie said:
Unless you have no choice heading directly into that sort of sea is a no brainier in my opinion far better to use a small jib and a combination of engine and sail and will be far less stress on boat and crew
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Well yes I did have a choice but my wife didn't want me to go on deck to put the main up when I should have put it up before leaving the mooring so I acknowledge I made wrong choices but that wasn't really what the post was about.

Poey50 think you're right about the fouling - I think I should replicate the situation next year with clean hull and prop before considering change of pitch.
 
Hmm, well, Featherstream are real experts at this stuff (and extremely responsive) so personally I'd ask them! (Although first you need to find out how fouled the prop is, that could well be the only problem.)
 
Increasing the pitch will have the opposite effect to that which you desire. "grip" really means thrust and your lower pitch ratio will give you more thrust but lower top speed. It should however give you more thrust for the same input torque at lower speed.(tugs use very low pitch ratios)

If as you say the combination of pitch and diameter gives max RPM and close to "hull speed" in flat water then leave well alone and give the prop a clean. Stalled blades give very little thrust.
 
Just for reference our 32 has a 16 by 12 two bladed folding prop.

This is the normal size fitted to the Bukh 20 we had.

Motoring into a wind over tide head sea we might expect no better than about 4 knots through the water. Don't know the rpm, but the limit was the boat's behaviour (crashing and plunging) rather than the engine power.

Motor sailing about 20 degrees off the wind might achieve a faster through the water speed, as much from lengthening the effective wave length encountered as anything else.

And just sailing on our ear in the same conditions we might get 6 knots through the water, but obviously no better than 4 knots vmg direct to windward.
 
Since you'd be changing the 3600 commisioning revs,presumably signed off as required by Beta perhaps you should consider if you're losing any benefit of the 5 year warranty provided.(although if you read this it is surprisingly limited).
 
sailorman said:
Why did the OP drop 1.5" in dia, especially with a feathering prop, the downside of the Featherstream is a very large boss thus reducing the blade area even more
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No, went from 15.5" 2 blade fixed to 16" 3 blade feathering - even accounting for larger boss, blade area increased. 16" is limit for S32 to give enough clearance to avoid cavitation.

Darglow happy to provide exchange cassette to change pitch and what effect it will have but stop short of saying whether they think its a good idea - as I would in their situation!

My conclusion is to wait until relaunch with a clean hull and prop and find some steep chop and head wind I can motor into (not usually difficult outside Plymouth Harbour) and repeat experiment. Actually I think I will try and do some comparisons of a) motor only into wind/sea; b) motorsail with main only; c) sail as high as possible, therefore at narrow angle to waves but with motor assistance to see how VMG compares. Interesting to speculate how forces of wave, wind and tide act on hull at different angles and compare to actuals.
 
eddystone said:
A couple of years ago I had a Beta 30 fitted to my Sadler 32. Probably 25 would have been optimum but that needs an alternator upgrade which more or less wipes out the small price difference and others who had the same engine fitted to same boat recommended it over the 25. The 2 blade 15x12 fixed prop was replaced with a Featherstream 16x10.5. That's a pretty fine pitch and the reason was so that the engine could reach maximum or near revs (3600) at full throttle. No problems so far but last week was probably the first time I'd motored into a steep sea head to wind and progress was predictably slow, I mean 1.5 to 3 knots at 2500 revs (Actually it was completely stupid I could have made similar time reefed down with maybe 3 long tacks but that's another issue). The Sadler has a short WL so probably pitches more than modern boat of same OL and indeed it sounded like propeller was scrabbling for grip much of the time. Another pertinent fact is that I'm sure the prop is quite significantly fouled - it didn't move off the mooring from mid-March to early August. Notwithstanding that I wondered if I should change the pitch to get more grip - changeable pitch is one advantage of the Featherstream. Darglow says the next increment would result in max throttle achieving 3200 instead of 3600 rpm. I rarely use more than 3000 - is there a downside to this?
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To be clear, would the engine only do 2500rpm?

Motoring head on into a chop takes a lot of power. That means using a lot of rpm if you want to get anywhere at all quickly.
It's not pleasant. sometimes if you drive faster, you have more control to avoid the worst lumps of water.
Small jib and a couple of reefs generally a better idea.
I'm not a great fan of motorsailing generally, but using the motor to cheat can let you luff around waves that might otherwise stop you.
Hull and prop fouling can cost a lot of speed. I think it's been a high-growth year for slime.
Also a lotof us haven't done the hours at the helm this year, and looking at my race results, it shows!

I wouldn't rush to change anything, just file away the data for now.
 
I installed a beta 25 and a new Featherstream prop on my Westerly Storm last year. I was a bit disappointed with the performance.
With my old VP 2002 and a 2 blade prop at 2750rpm I could get nearly 7 knots on a calm day and slack water, only about 6.5 with the new engine and prop.
I contacted feather stream and they sent me a free replacement cassette to increase the pitch.
It was easy enough to change but, as I have not launched the boat this year I don't know how much better it will perform.
Out of interest do you get chattering when motoring along at tick over?
 
eddystone said:
My conclusion is to wait until relaunch with a clean hull and prop and find some steep chop and head wind I can motor into (not usually difficult outside Plymouth Harbour) and repeat experiment. Actually I think I will try and do some comparisons of a) motor only into wind/sea; b) motorsail with main only; c) sail as high as possible, therefore at narrow angle to waves but with motor assistance to see how VMG compares. Interesting to speculate how forces of wave, wind and tide act on hull at different angles and compare to actuals.
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Good plan! My money, from trial and error, would be be on mainsail plus engine to give the best VMG as you can point higher. I've done this several times down the western Solent when in a hurry. You can probably get away without a reef under under Bft 6 apparent as it is quite a small sail on the 32. Reefed genoa and main (sans engine) are slower VMG in my experience, as further off the wind to fill the genoa, but still able to punch through the chop. And then it counts as proper sailing. I hope you report back.
 
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KREW2 said:
I installed a beta 25 and a new Featherstream prop on my Westerly Storm last year. I was a bit disappointed with the performance.
With my old VP 2002 and a 2 blade prop at 2750rpm I could get nearly 7 knots on a calm day and slack water, only about 6.5 with the new engine and prop.
I contacted feather stream and they sent me a free replacement cassette to increase the pitch.
It was easy enough to change but, as I have not launched the boat this year I don't know how much better it will perform.
Out of interest do you get chattering when motoring along at tick over?
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That's strange - I had a VP2002 with a 15.5x12 2 blade prop originally and struggled to get 5 knots with a favourable tide. New set up much better and the slight fear I had about the feathering blades not reversing has turned out not to be; in fact although I still have enough prop walk in reverse to be useful reverse is noticeable better. It's also less painful to the ears than the VP2002 - (also put in new sound insulation to replace old foam). I think chattering at tick over is a normal diesel characteristic - smooths out at higher revs.
No can get 3,600 or thereabouts if I want but 2500 is my normal cruising speed; if you look at fuel consumption curve, 2.4lph at 2400, 6.0lph at 3600 for small gain in speed.

Anyway, won't do anything until seen what clean prop will do. One more trip this year planned so I'm thinking what I can attach to the end of a pole to knock the looser stuff off the blades without doing any damage - maybe a narrow plastic scraper.
 
When trying to make ground into a strong wind and choppy sea under motor, I’ve found that it helps a lot to simply bear off the wind a little. That effectively lengthens the wave length and makes for a smoother motion plus you generally find that the speed increases. Obviously not possible in confined waters but worth bearing in mind if space permits.
 
eddystone said:
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No can get 3,600 or thereabouts if I want but 2500 is my normal cruising speed; if you look at fuel consumption curve, 2.4lph at 2400, 6.0lph at 3600 for small gain in speed.
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But motoring into strong chop is not normal cruising, so normal cruising RPM is out the window.

Also the fuel consumption at any RPM will be a function of the work the engine has to do. If you need to fight chop, you will be using more fuel. Achieving a low lph figure is not much gain if you are making little progress and not enjoying it. These circumstances are what we fit half decent engines for. Use the power.
Unless it's drier and more comfortable to go slowly and you're in no rush of course.
Drag from slime and weed, plus reduced prop efficiency from the same will also up your fuel consumption.
 
eddystone said:
That's strange - I had a VP2002 with a 15.5x12 2 blade prop originally and struggled to get 5 knots with a favourable tide. New set up much better and the slight fear I had about the feathering blades not reversing has turned out not to be; in fact although I still have enough prop walk in reverse to be useful reverse is noticeable better. It's also less painful to the ears than the VP2002 - (also put in new sound insulation to replace old foam). I think chattering at tick over is a normal diesel characteristic - smooths out at higher revs.
No can get 3,600 or thereabouts if I want but 2500 is my normal cruising speed; if you look at fuel consumption curve, 2.4lph at 2400, 6.0lph at 3600 for small gain in speed.

Anyway, won't do anything until seen what clean prop will do. One more trip this year planned so I'm thinking what I can attach to the end of a pole to knock the looser stuff off the blades without doing any damage - maybe a narrow plastic scraper.
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I was told by Darglow that at 15x18 my 2 blade prop was oversized. Max revs on the VP 2002 were 3250, I could not go over about 2800, but just under 7 knots at 2500 I considered very satisfactory. Taking it up to 2800 just dug the stern in, and just under 7knots must be the maximum hull speed, so no need for more revs
I changed the Volvo because it was getting hard to start. The Beta is smoother quieter, and starting on the button is a luxury to me, and 6.5 knots is okay.
Darglow are familiar with the "Chattering" as they called it. They said others with Beta engines had noticed it, and it was something to do with the Beta not having a large flywheel, and on tick over in gear the prop wasn't sure whether to feather or drive causing the chatter. As you say take the revs up to a 1000 and it goes. They suggested a coarser pitch should stop the problem which made sense, as it doesn't chatter when idling, not in gear.
They sent me a new cassette, which I have put in. Hopefully, it will solve what is a minor issue, but I wont find out until next spring, I hope.
 
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TernVI said:
Also the fuel consumption at any RPM will be a function of the work the engine has to do. If you need to fight chop, you will be using more fuel.
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Are you sure or am I reading it wrong? Are you saying that if I run the engine at 2000 rpm and motor with the wind at say 6 knots of speed (stw) and then turn the boat against the wind with a drop of speed at 5 knots the consumption will increase? Why? I would expect that only if you increase rpm in order to maintain the 6 knots will increase the consumption.
 
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