B 28 Propellers

[Gregostar]

Hello everybody

I would like to upgrade the performance of my 28 is I think the propellers are there for a lot

Currently my 28 is equipped with 17x21 4 blades and 1 3/8 "shaft in Aqualoy

Motorized with 2 Yanmar 6LPAM-STP coupled ZF Hurth 63-A ratio 1.6

Cruising speed 21.5 / 22 Kts @ 2800 and 23.5 / 24 Kts @ 3000

Next month new botom paint for further testing

I do not seek to sail at 40 Kts but have a higher cruising speed of the type 24 Kts for 2500/2600 to have a better consumption

In general I sail 100/130 nautic per fishing trip

Do you think replacing the propellers could give me that performance?

Thank you for your reply

[Yannis]

I have no idea.
However, there must be something that you should change in your overall configuration, because I have EXACTLY your performance data, as you just described them, but I only have 240's, not 315's.
Is it the props, is it the bottom, the weight, there must be something !

Good luck.

[Tony Meola]

First question is do the engines hit their top RPM numbers? If they don't then there is probably a prop issue.

Is the bottom clean?

How much extra gear are you carrying? Perhaps the boat needs to go on a diet.

Are you running with a tower, no tower? Wind resistance is always a factor.

If you do a search you will see many posts by Bob Lilco about tweeking props.

Are these engine numbers correct, 315 HP.

[Bill Fuller]

Greg,

First you need to understand your motor. It is completely different than Yannis or my 4LHAs.
Your 6LPAs are not designed to cruse at 2400-2600 RPM. They are designed to cruise at closer to 3500 RPM.
Your motors are rated to produce 315 HP at 3800 RPM and the Yanmar specification is for them to turn about 4000 RPM with your boat fully loaded.

So, first thing is take your boat out and get it warmed up and them open the throttle all the way and see what RPM you can turn. Any less than about 4,000 and you will need to reduce the pitch. with 21 inch of pitch you have a theoretical speed of 42+ knots at 3800 RPM. I would be surprised if you need to had pitch. More likely you will need to remove pitch, maybe all the way down to 17x17.

Let us know what your wide open RPM is and then we can go from there.

Bill

[Bill Fuller]

Greg
go here to see the Yanmar specifications for your motors.

https://imgur.com/a/jCz3r

ill

[Gregostar]

Hello everyone and thank you Bill for the information

In 15 days I leave the boat for bottom paint

then I would test at full speed/max RPM

I will also test the photo tachimeter to determine the error of my instrument because aparament it is always false and test the rpm max no load

Then I ask myself if I would not have a separator filter too small, I use a racor type 500g for each engine, if people have fuel separator what model you use for the 6pl's

Thank you