Prop advice please.

[Gladiateur]

I have a two blade folding Volvo Penta prop 16 x 11 on a 33ft 6 tonne sloop. I would like more drive from the prop and wondering if I can fit higher pitch blades to the hub or should I be thinking of replacement?
Struggling to get advice from VP.

 

[RivalRedwing]

The prop should be matched to your engine and gearbox hence it is unlikely that adjusting the pitch will have much effect. Replacement with a 3-blade prop will likely give you more drive, a fixed blade will be cheaper than a folding prop but if you appreciate the additional speed that a folding / feathering prop brings when sailing then you could do worse than look at a 3 blade Featherstream from Darglow.

 

[Stemar]

You can find out what your theoretical ideal prop is using the calculator here:

Free to use Propeller Sizing Calculators

 

[johnalison]

I have a Volvo 2-blade folding prop on my boat of similar size and 27hp motor. I found the prop adequate but in retrospect I would have preferred the 3-blade. A friend with an almost identical boat seemed to motor faster and more easily with the same engine and 3 blades. I read that the Volvo 3-blade will allow motoring at 400 rpm less for the same speed. I assume that will give more punch into a head sea too but don’t have direct experience.

 

[Tranona]

I have a two blade folding Volvo Penta prop 16 x 11 on a 33ft 6 tonne sloop. I would like more drive from the prop and wondering if I can fit higher pitch blades to the hub or should I be thinking of replacement?
Struggling to get advice from VP.

Yes, you can by different pitch blades, but more information is needed before suggesting whether it is worth doing it. I assume you have a 30hp engine and if it is a Volvo then a 16*11 is a common size for that size boat. If you post details on the actual boat and engine/gearbox and what you want to achieve or fell what is currently inadequate you might get better advice.

 

[Gladiateur]

My boat is a Wauquiez Gladiateur 33. Engine is a VP MD2030-D, saidrive MS25S-A. I would like to get six knots at 2000 revs or less preferably. I dont think this is unreasonable.

 

[Gladiateur]

The prop should be matched to your engine and gearbox hence it is unlikely that adjusting the pitch will have much effect. Replacement with a 3-blade prop will likely give you more drive, a fixed blade will be cheaper than a folding prop but if you appreciate the additional speed that a folding / feathering prop brings when sailing then you could do worse than look at a 3 blade Featherstream from Darglow.

Thanks will check them out.

 

[Tranona]

My boat is a Wauquiez Gladiateur 33. Engine is a VP MD2030-D, saidrive MS25S-A. I would like to get six knots at 2000 revs or less preferably. I dont think this is unreasonable.

No you won't get that without severely overpropping. The engine is rated to 3600rpm with cruising revs +/- 2400 to give you around 5.5 knots. 16*11 is the correct size and you should be able to achieve 7.5 knots at between 3400-3600. You could increase the pitch by 1" which will bring the revs down by approx 250 for any given speed but you need 15hp to get 6 knots and at 2000rpm the engine is only capable of producing 12hp. So a 16*12 would likely give you your 6 knots at 2400, rather than 5.5knots with the current propeller.

If you want to check out actual figures rather than my estimates, carry out a series of runs in flat water at 200rpm intervals from 1800 up to maximum to give you a plot. Then use the 250 change for 1" pitch estimate to determine what you will actually achieve by increasing pitch. If it helps I ran a 2030 for over 3000 hours and the optimum cruising revs were as predicted by the power curves at 2400rpm.

 

[Gladiateur]

No you won't get that without severely overpropping. The engine is rated to 3600rpm with cruising revs +/- 2400 to give you around 5.5 knots. 16*11 is the correct size and you should be able to achieve 7.5 knots at between 3400-3600. You could increase the pitch by 1" which will bring the revs down by approx 250 for any given speed but you need 15hp to get 6 knots and at 2000rpm the engine is only capable of producing 12hp. So a 16*12 would likely give you your 6 knots at 2400, rather than 5.5knots with the current propeller.

If you want to check out actual figures rather than my estimates, carry out a series of runs in flat water at 200rpm intervals from 1800 up to maximum to give you a plot. Then use the 250 change for 1" pitch estimate to determine what you will actually achieve by increasing pitch. If it helps I ran a 2030 for over 3000 hours and the optimum cruising revs were as predicted by the power curves at 2400rpm.

Happy to accept your estimates, to be honest I havent revved over 2k very often. Will try and get some 12 blades priced up and will be giving her a bit more welly this season. Thanks.

 

[johnalison]

Happy to accept your estimates, to be honest I havent revved over 2k very often. Will try and get some 12 blades priced up and will be giving her a bit more welly this season. Thanks.

My engine instructions, same engine, say that the ideal running speed is the max revs minus 400 rpm, ie around 3000. I think that most of us will find this much too high and I think that Tranona's 2400 is nearer the mark. In my slightly lighter boat of 5.4t that was my most usual speed for passage-making and gives me around 6.4kn. With a clean bottom in still water more than 5m deep I get around 6kn plus 0.1kn for every 100 rpm over 2000. I have only occasionally run at 3000, such as when being told to hurry by Dover harbour, but have often run at 2700 when I need to push against wind and sea. On one occasion I ran at 2700 for 24 hours when returning from Ireland with only short breaks to check oil and water filter. This is likely to be better for the engine than running it too slowly, so I am told.

 

[Tranona]

Happy to accept your estimates, to be honest I havent revved over 2k very often. Will try and get some 12 blades priced up and will be giving her a bit more welly this season. Thanks.

Running at low revs like that leads to coking up the exhaust elbow prematurely. These little engines like running hard and 2400 is the "ideal" as it is peak torque and lowest specific fuel consumption. Periodically run it hard - 3000 plus for 20 minutes to help burn off deposits .

 

[Gladiateur]

My engine instructions, same engine, say that the ideal running speed is the max revs minus 400 rpm, ie around 3000. I think that most of us will find this much too high and I think that Tranona's 2400 is nearer the mark. In my slightly lighter boat of 5.4t that was my most usual speed for passage-making and gives me around 6.4kn. With a clean bottom in still water more than 5m deep I get around 6kn plus 0.1kn for every 100 rpm over 2000. I have only occasionally run at 3000, such as when being told to hurry by Dover harbour, but have often run at 2700 when I need to push against wind and sea. On one occasion I ran at 2700 for 24 hours when returning from Ireland with only short breaks to check oil and water filter. This is likely to be better for the engine than running it too slowly, so I am told.

Thanks what prop are you running?

 

[johnalison]

Thanks what prop are you running?

Volvo 2 blade folding, as I said earlier .

 

[doris]

The prop should be matched to your engine and gearbox hence it is unlikely that adjusting the pitch will have much effect. Replacement with a 3-blade prop will likely give you more drive, a fixed blade will be cheaper than a folding prop but if you appreciate the additional speed that a folding / feathering prop brings when sailing then you could do worse than look at a 3 blade Featherstream from Darglow.

I bough just that from Darglow a couple of years ago. A great product from a terrific company.

 

[Tranona]

I bough just that from Darglow a couple of years ago. A great product from a terrific company.

While I agree - I also have a Featherstream - it is not necessarily appropriate for the OPs boat which is an IOR style cruiser racer with a 30hp Volvo saildrive - more than enough power. He already has the correct prop, but his aim is to reduce cruising revs which can only be achieved by over propping. Another 1" pitch on the prop will drop revs by around 250 but his target of 6 knots at 2000rpm is unachievable.

 

[DJE]

Another vote for the Darglow Featherstream. When I bought mine - a good few years ago - it was pitched perfectly to allow us to achieve maximum engine power as we requested. But they included the option of one free pitch adjustment if we felt we needed it. The prop is also arranged to have a flatter pitch in astern which I find very effective.