Mahe 36: Sail Drives and Props

[Edmund]

Tested again, in more correct conditions. Just minor changes.
Now also including idle. Idle speed does feel quite a bit higher, but I forgot to test idle with the 17x12. A bit late now.... Anyone else who have a good number?

Two engines:
Prop: RPM: Knots:
18x13 850 3,1

17x12 2400 7,9
18x13 2400 8,6

17x12 3250 9,5 top
18x13 2950 9,6 top

One engine:
Prop: RPM: Knots:
18x13 850 2,1

17x12 2400 7,0
18x13 2400 7,5

17x12 3050 8,2 top
18x13 2650 8,2 top

[DotDun]

Just curious as I'm asking out of ignorance.

I've always been told that a proper sized prop will allow the engine to reach 'just-short' of redline/top rpm. If you can't achieve that, you are overloading the engine.

By using a bigger prop it's obvious you can achieve a higher speed at the same rpm. But, you'll certainly be burning more fuel...???? (nothing is free)

I would think a target speed/rpm would be a ~1/2kt less than hull speed at an rpm that achieves max torque vs. fuel consumption.

Just asking as I've often thought about playing with size/pitch on my boat.

[colemj]

That is correct. Edmund has simply over-propped his boat to get higher boat speeds at lower rpm, as evidenced by no increase in top speed, but no ability to reach rated rpm. He will not get better fuel economy, as there is no free lunch. The fuel/rpm graphs from Volvo are for a perfectly matched prop and are not valid otherwise - they will change for an over-propped situation. He is also outside of Volvo's explicit instructions on sizing a prop vs WOT rpm's the engine must be able to reach.

Frankly, I do not understand his need or reasoning, as the boat seemed perfectly propped with the old props.

Mark

[Edmund]

According to Volvo, the D1-30 should be propped to reach a max RPM between 2800 and 3200. The 3250-3300 reached with the props installed by FP are too high, and I think the 2950 I now get with the 18x13 are the optimal max RPM.
I do not agree that I have over-propped, I do think FP is under-propping.

Volvo Penta have admitted they have no calculator or table for selecting props for catamaran sailboats. I asked Volvo Norway to calculate prop for the 1/2 of my boat, with one engine, and the result was the propsize I have now mounted

I can now achieve my previous cruising speed at only 2200rpm, 200 less than before, and probably thereby even save a little bit fuel/Nm. More important is the noice saved.
Or I can increase cruisingspeed, at the same RPM as before. I will for sure burn a bit extra fuel/h, but not so much pr Nm. And as I've said before: The extra speed is important to us, we have a 40 Nm/5h long fjord we normally need to propell our way out of before we can start sailing.

Edmund

[colemj]

My mistake. I thought the D1-30 was a 3600rpm engine and now see that it is 3200rpm. So you were underpropped.

Mark

[Seastream]

Mark, will those zinc collars fit any saildrives mated to Volvo D1-20 engines on Mahes? I want to replace mine but can't find part numbers in the pile of paperwork onboard.

[Cotemar]

Originally Posted by Seastream

Mark, will those zinc collars fit any saildrives mated to Volvo D1-20 engines on Mahes? I want to replace mine but can't find part numbers in the pile of paperwork onboard.

Sail Drive Split Ring Zincs Volvo Penta part # 3888305
130 Saildrive Split Ring Zinc Anode
Outside Diameter: 4", Inside Diameter: 1-3/4", Weight: 3.4 lbs
BoatZincs.com $44.37
www.marinepartsexpress.com $52.77

Prop Zincs Volvo Penta part # 3858399
3-Piece Collar Propeller Zinc Anode
BoatZincs.com $24.59
www.marinepartsexpress.com $35.71

[Seastream]

Forgot to ask before: Is there a different part number for zincs used with fixed vs folding props?

[Cotemar]

Originally Posted by Seastream

Forgot to ask before: Is there a different part number for zincs used with fixed vs folding props?

Maybe this will help.

Propeller Anodes for Volvo Penta

[Seastream]

Another Q: We lost a blade off one of our Volvo folding props while sailing our Mahe up from Tortola. We couldn't find it. Is this something a propeller repair/maintenance shop (such as New Englands H&H propeller) can replace or need we obtain a replacement blade from Volvo. I was thinking to change to fixed three blade props but in reading this thread through, see that vibration can be an issue.

[Seastream]

Hi Al. Bob here. I just bought and sailed hull 91 from Tortola to NH last May. I just changed out the saildrive fluid with ATF prior to in water winter layup. It appears I should've used 15-40 oil. Crumbs. I guess it won't hurt (won't be using the boat til spring), but if I'd have known, I'd have used oil...simpler, as that's the same as the engine oil. I wish Volvo could make up their mind.

[DtM]

I think you have to go with your local Volvo mechanic's recommend

[Cotemar]

Originally Posted by Seastream

Another Q: We lost a blade off one of our Volvo folding props while sailing our Mahe up from Tortola. We couldn't find it. Is this something a propeller repair/maintenance shop (such as New Englands H&H propeller) can replace or need we obtain a replacement blade from Volvo. I was thinking to change to fixed three blade props but in reading this thread through, see that vibration can be an issue.

Here is the info you need to buy a replacement blade.

http://www.cruisersforum.com/forums/...tml#post355570

Most likely you will have to buy there 3 blade kit.

http://www.marinepartsexpress.com:80...o.x=12&Go.y=12

[Wayneleblanc]

We have the original two blade props the boat came with. They have performed flawlessly. We are in our fourth year of cursing with them.

[DtM]

Flawless and cursing !!!!!

Sorry, just made me laugh.