Prop size for Lagoon 450, Leopard 48 etc?

[Bahia]

Hi guys,

I am repowering my Bahia 46 with Yanmar 4 Cylinder 53hp and SD60 standard.
I had 3 cylinders before... so now I will need bigger props... what would be a good size?

Best regards,
Bahia

[Cotemar]

Bahia,

Not sure if this will help.

The FP Helia 44 has 3 bladed 18X16 Props on the Volvo Penta D2-55 Saildrive Engines

18" Dia. X 16" Pitch Left Hand (Counter Clockwise)

[westwinds]

I have a book on selecting propellers by Dave Gerr, but it gives no information on a cat. I do not believe the standard equations would work because the beam on the hulls are narrow and the length is long on a cat compared to a mono. What I would do is first look at the tip clearance from propeller to bottom of hull, subtract 2 inches for clearance (other wise you get vibration from water turbulence from the propeller tips whacking the bottom of the boat) and go with that for maximum new diameter, if within reason. By the way, are you using the same transmissions? If not there could be some adjustments needed for different gearing reductions. What I would do is use an adjustable propeller and keep trying different pitches until engine loading and RPM work out for peak power. Here are several manufacturers:

Ewol adjustable propellers
EWOL Propeller

Under sail the MAX PROP will increase sailing speed by about 15%, the largest difference being noticed when sailing in light air.
MaxProp - automatic feathering propellers worldwide production leader

Talk with either of these propeller sources and see what they recommend for your boat make, new engine size and room for larger propeller.

[Bahia]

Hi guys,

thank you for your input.

However I actually want to get a 3-blade fixed prop.
I don't need no trouble with the folding props.

Best regards,
Bahia

[Bahia]

@Cotemar:

I followed your guidance and ordered 18x16 3-blade props for my Bahia.

Already excited how fast she's gonna fly.

[Shrew]

Are you sure you need props larger in diameter? Or simply a different pitch. The space between the hub of the prop and the hull wouldn't theoretically change.

Typically an increase in HP is coupled with a change in the pitch of the prop, while the diameter typically remains relatively the same.

Props are typically measured (<Diameter> X <Pitch>)

[Bahia]

Hi,

well I have increased engine displacement by 50%
so just a change in pitch wouldnt be enough...
Therefore I went for a bigger prop.

The SD60 saildrive can take up to 21"... and the 18x16 fits just fine



Cheers

[Cotemar]

Originally Posted by Bahia

Hi,

well I have increased engine displacement by 50%
so just a change in pitch wouldnt be enough...
Therefore I went for a bigger prop.

The SD60 saildrive can take up to 21"... and the 18x16 fits just fine



Cheers

That is some FINE looking KIT right their.

[Bahia]

Hi,

I've finally finished all my fitments etc. and took her on a trip.

After the first 10 hours of engine operation I tried WOT for a half a minute... And I noticed that I can't reach 3000rpm. I can reach maximum 2700rpm under load. IN neutral it revs up to 3000rpm.

So it means I'm a bit overpropped. Which is strange... as the Volvo D2-55 runs with the same prop... And I have 53hp. Can it be that much of a difference?

I mean I don't complain. With new antifouling I am running at 10knots now at 2500rpm

Should I be worried... or just let it be.

Thanks
Rod

[westwinds]

Originally Posted by Bahia

Hi,

I've finally finished all my fitments etc. and took her on a trip.

After the first 10 hours of engine operation I tried WOT for a half a minute... And I noticed that I can't reach 3000rpm. I can reach maximum 2700rpm under load. IN neutral it revs up to 3000rpm.

So it means I'm a bit overpropped. Which is strange... as the Volvo D2-55 runs with the same prop... And I have 53hp. Can it be that much of a difference?

I mean I don't complain. With new antifouling I am running at 10knots now at 2500rpm

Should I be worried... or just let it be.

Thanks
Rod

Just let it be. Dave Gerr's book on propellers says 10 percent over propped will not harm the engine and you have larger engine so there should be plenty of power.

[Bahia]

Thank you, westwinds. I was thinking the same. It's just 10 percent and I have enough power reserves. Even during light cruising I can maintain at least 1800rpm which is not too low for this type of engines.

[EWOL Props]

Originally Posted by Bahia

Hi guys,

I am repowering my Bahia 46 with Yanmar 4 Cylinder 53hp and SD60 standard.
I had 3 cylinders before... so now I will need bigger props... what would be a good size?

Best regards,
Bahia

Hi Bahia,

be careful, the SD60 is the first S-Drive that can have 2 different gear ratios: 2.23:1 or 2.49:1 (previous versions had just one ratio possible).
Depending on which one you have on your boat, you will obtain a different prop size.
I guess your engines have a max of 3000 rpm, in which case we'd recommend a 19" for the 2.23:1 and a 20" for the 2.49:1.
Please check you have sufficient room available under the hulls.
Anyway....you can calculate it yourself at www.ewoltech.com

[Bahia]

Hi,

I've got the standard ratio of 2.23:1... And I went with 18x16 as I mentioned a few posts above...

Cheers
Rod

[VERTIGO]

Just wondering on how the props were working out? I had a set of 3 blade fixed Volvo on my 440 and found them to be awesome! Until one fell off. True story. I boat on the Chesapeake bay and if a crab pot came within 10 feet of me it sucked into the prop, no less than 5 times last summer. I love to sail at night but it made it virtually impossible.

Just kinda curious how your set up is working, everything I read says not to over prop, if I do the calculations I think you could lose an inch but probably better to lose 2 on the pitch. Between the overworked engine, lost power on the low end and lost fuel I would recommend to make the switch and bite that bullet.

I did change mine out for Flex-o-fold and love the performance under sail as well as motoring. I only put one on originally and left the Volvo on the other side. Forward performance was identical, took some getting use to with the reverse. Plenty of power but have to come in slower, no "stopping" power. Once slow enough the grab is close to the fixed.

SV BlackSheep
440 Lagoon Hull#81

[Bahia]

Hi,

the props are actually running great. Can't complain so far.

Cheers