Volvo 2002, revs & propellor question

[john_travers]

Am I suffering engine paranoia?
Boat Westerly Fulmar.
Handbook states max revs 3200. I never rev it past 2600 ( I dont really know why other than I think it will blow up if I do) but at 2600 revs with the current prop fitted boat speed is only 5 knts in flat water.
I think it should be nearer 6 Knts but not sure.
Propellor not marked so I dont know the size & pitch but it does look on the small size.
Before anyone asks the bottom is clean.
Should I try another prop or rev the engine harder?
All advice gratefully received.

 

[Robin]

Something isn't right by the sound of it. Assuming your boatspeed figure is correct and not under reading, the Fulmar I would expect to be capable of 7kts plus flat out in flat water.

The engine should be able to pull max revs under load in gear - just. If it can rev to maximum or above easily in gear the prop is too small in diameter or pitch or both. If it cannot reach max revs in gear the opposite is the case.

Generally speaking boatyards seem to err on the side of too great a pitch/dia and certainly Westerly used to do that, meaning you get more speed at lower revs at the expense of being able to achieve max revs (and max horsepower), which you need for strong head winds/seas. In your case though the prop sounds as if it might be too small, has it been changed from the original, maybe to a folder or 2 bladed for extra speed under sail?

Almost certainly the dia/pitch of your prop IS marked on it somewhere, usually stamped on the boss and maybe hidden under the nut. You could give boat details and engine/gearbox details to one of the prop makers who will tell you roughly what the correct size should be, though remember the answer will be slightly different for 2 blades versus 3 blades.

 

[LeonF]

John there were 2 posts re this issue... mine under volvo revs and another in the past week..have a look at the replies.

 

[Eccles]

Interestingly my local Volvo dealer said that when specing props for sailors he always slightly over pitches them on the basis that yachtties spend alot of their time motor-sailing and with the assist from the sails the load on the engine is then about normal. Don't know how sound his argument is. My Moody 31 (Volvo 2002 with two bladed prop) max revs under load is about 2600. I cruise a 2200 and get 5.5 in flat sea.
When I win the lottery I'd love to see what a 3 bladed Brunton would do for the speed (under power and sail) and the vibration.
Jonathan

 

[andy_wilson]

My Fulmar (fin) has same engine. Sadly unsure of prop size.

When hull and propellor are immaculate, in flat water, give or take a bit:

2,500 rpm = 5.5 kn
2,800 rpm = 6.3 kn
3,200 rpm = 7.0 kn

It doesn't take long in the water to knock these figures back a bit due to fouling.

Don't be afraid to give it a blast, I try to ensure at least a few minutes at full power at some point of every trip. Ocassionally we have gone for miles at full chat or at least 3,000 rpm+.

Give it a treat.

 

[john_travers]

Re: Volvo 2002, revs & propellor question

Many thanks for the advice. I will try running the engine at higher revs and see if I get max hull speed at max revs.
Still think it will shake itself to bits!

 

[philip_stevens]

Re: Volvo 2002, revs & propellor question

From http://www.mywesterly.co.uk/

The original specs for the Fulmar.
Engine-VP 2002 Gearbox-2.4:1 Shaft-25mm Prop-15"x11" Blades-2 Rotation-LH

I have a VP2003 on my Konsort Duo, and am not afraid to run it at full bore. In fact, it does a diesel more good than harm.

If you want more advice on the Fulmar in particular or Westerly's in general, go the the Westerly website http://www.westerly-owners.co.uk/index.html and join the newsgroup.

 

[ayearsley]

Re: Volvo 2002, revs & propellor question

Did speed trial yesterday in my Fulmar 417, 6 weeks afloat in Menai Straits so perhaps a little dirty. Results by log as follows-
1700 revs 4.5 knots
2000 5.1
2500 5.9 but perhaps 6.2 by GPS both ways at slack
2800 6.2
3050 6.4 at full throttle
Prop is 15 by 12.5 36% which replaced the original 15 by 11 25%. This would not absorb the full HP. New prop gives much lower revs for same speed, particularly when motor sailing.
Both props are 2 bladed. GPS indicates perhaps a small under reading on the log.
Tony

 

[philip_stevens]

Re: Volvo 2002, revs & propellor question

I changed the 14x13 2 blade prop on my Bukh engined Konsort for a 3 blade 15x13 that was taken off a Bukh engined Fulmar when the owner fitted a Brunton prop on his replacement Vetus.

I cannot say how the Brunton/Vetus improved the Fulmar, but I do know that my Konsort was transformed in ahead, and would stop much quicker in astern. By transformed in ahead, I mean she would punch her way into head seas without losing much way. In astern, she would start to, and go astern to where I wanted, and not where the prop-walk wanted to take her. Full ahead, I could not quite get 7 knots. With the 2 blade, I was lucky to get 6.5 knots.