Mainship 400 - Will this prop work on my boat?

[jefndeb]

Hello,

I have a friend who has a 24 inch prop for sale, (attached is the data sheet on his prop he has available,)

I don't have any data on my prop on this 2006 Mainship 400, I have a single Yanmar 6LY2AN-STP 440hp..

I think mine is 24 inch as well but not 100% sure it's size, bore or pitch...or rotation LH or RH, I feel real ignorant not knowing this info.

Anybody know what would normally be installed on my trawler?..also attached is a picture of my current installed prop, taken during haul out...

Here is some info from the data sheet.

24 inch Prop
4 blade
2 Inch Bore
Pitch 30.713
LH Rotation
Weight 47 lbs
Material - NiBral

Manufacturer - Huna Shen

I also added a picture of the data plate on my ZF Transmission..

Thanks for comments..

 

[Nomad Willy]

It says there’s more pitch than diameter. Usually only found on extremely fast boats. And pitch is measured in inches not to three decimal places.

Looks like it would take more than 440hp to turn this prop w so much blade area.

Prop is RH rotation.

I like the struts.

Just observations ....

 

[rslifkin]

It's most likely too much prop, but how much remains to be seen. Based on the Michigan Wheel calculator, a target WOT RPM of 3400, 440 hp, 2.5:1 trans ratio and a wild guess of 18 kts top speed, they indicate an optimal 5 blade prop would be 28x23. With 24" diameter, they suggest 26" pitch.

So this prop would need to be de-pitched, but after that, probably wouldn't be too crazy. Considering what they're suggesting for diameter (28" for 4 or 5 blade, 31" for 3 blade) the high blade area in a 24" might not be excessive. It's probably a bit more blade area than needed, but not by a lot.

To help us figure out a little more accurately, how fast does your boat run with a single 440hp?

 

[jefndeb]

I usually go about 8 to 9 knots and 2300 to 2500 RPM

 

[rslifkin]

I usually go about 8 to 9 knots and 2300 to 2500 RPM

What does it do for speed at WOT? That's what matters for prop sizing.

 

[DavidM]

I would be very careful about potentially over propping your engine with that prop. Tony Athens recommends propping to 3,550 rpm with that engine and never running it at more than 2,800 rpm for long.

I would take that spare prop to a good shop, have them true it up and run it through their prop calculator to see if it will rev to 3,550 rpm with your boat, engine and transmission. Kind of doubtful as others have said if it is 24x30.7.

David

 

[rslifkin]

I would be very careful about potentially over propping your engine with that prop. Tony Athens recommends propping to 3,550 rpm with that engine and never running it at more than 2,800 rpm for long.

I would take that spare prop to a good shop, have them true it up and run it through their prop calculator to see if it will rev to 3,550 rpm with your boat, engine and transmission. Kind of doubtful as others have said if it is 24x30.7.

David

I just re-ran my calc with a target of 3550 rpm. That now shows that for 18 kts boat speed and 24" diameter, optimal pitch would be 25". Probably too far off to re-pitch that prop, unfortunately.

 

[jefndeb]

Thanks for the input, I didnt buy it yet, didnt really think it would work since it came from a Bank cove 25 knot+ boat....but he is an old friend and asked me the best way to sell it and I thought I might could use it at first since I dont have a spare.....


He spend $1300 getting it re-worked.


Can you guys suggest a good prop size to target for a spare?..


I usually dont run above 2800, try to stay close to 2000 to 2500 ....

 

[rslifkin]

To ballpark a size for a spare prop, we need to know how fast your boat can go at WOT. And it wouldn't hurt to know what size prop you already have and what RPM it reaches at WOT with that prop.

 

[jefndeb]

OK, at 3300 RPM (WOT) I can under normal conditions, i can see 12-14 knots, I have seen 15 but that was probably tide/wind assisted...

 

[rslifkin]

Alright, I just ran some numbers through the Michigan Wheel calculator. I used 14 kts at WOT and the target RPM mentioned of 3550 and did a little research. It looks like your current prop should be 26" diameter. It looks like the 370hp Yanmars and 385hp Cats ran a 26x19.5 prop from the factory.

Your setup calculates out to wanting either a 26x22 3 blade or a 26x21 4 blade. Being that optimum diameter is suggested as 28" for 4 blade or 31" for 3 blade, I'd tend towards a 4 blade for the extra blade area.

That's probably a little less prop than your current setup if you're only hitting 3300 RPM now. In which case, it might make sense to put a different prop on the boat and keep your current one as the spare.

 

[jefndeb]

ok, so i should keep a look out for a 26 x 21 4 blade correct?