No change with pitch change

[Budman23]

Due to my recent post i ordered another prop yesterday it arrived with excitment i went to the the river ran a base line and then changed props but my top speed was exactly the same.......

87 force on a 15.5 foot bayliner capri

original prop was 12 5/8" 21p 3 blade

New prop is 13" 17p 4 blade

problems only 32mph (GPS)with both props, new prop has alittle more acelleration, Seems to be a bogging with a tube.

No tach Yet so no idea about WOT RPMS

I tried all the different trim settings on the manual tilt and not change in speed with either prop

All testing was done with a six pack and two adults only and a couple life jackets...

Is there any reason the boat doesnt change with the prop change? Shouldnt I be goin allot faster 45 mph???????? Any ideas

 

[Sea Rider]

Re: No change with pitch change

Yes, as in any boat/engine configuration, you should perform wot test with a tacho to see max rpm achieved with both props and see how less you are from max rpm rated for that given engine, so to play with pitch. If looking for max speed will lose hole shot and viceverse, you should have at least 2 props for different water activities. Tiny Tach has cheap, small, induction friendly to install tachos, get one and mount on dashboard and wot test.

Happy Boating

 

[Bifflefan]

Re: No change with pitch change

Well, you really do need a tach so you can see the RPM difference.
The 21p may have been to much and the motor just couldnt push it any faster, and the 17p is not enough and your RPM's are topping out.

What is the HP on the motor?

 

[metriccrescentwrench]

Re: No change with pitch change

For that size boat and engine the speed you saw is in the ballpark. If you find the perfect prop you might see a couple more mph, but possibly sacrifice hole shot and acceleration. And before spending any more time or effort playing with props definitely get a tach.

It takes a certain amount of power to push a boat through the water at a given speed. Just fer' instance, let's guess that your engine was turning maybe 4800 rpm with the 21 pitch prop, and 6000 rpm with the 17. The engine was making somewhere in the ballpark of the same power at WOT in each case, therefore you saw about the same speed. It's only when you get significantly outside of the engine's peak power band that you'll see a drop off in speed. With the lower pitched prop you'll have better acceleration, and the engine will live longer because it's not bogging down.

 

[steelespike]

Re: No change with pitch change

Does the boat seem to lay down flat like it is glued to the water regardless of the trim setting?Is the antivent plate(just above the prop)visable on plane?

 

[Budman23]

Re: No change with pitch change

Does the boat seem to lay down flat like it is glued to the water regardless of the trim setting?Is the antivent plate(just above the prop)visable on plane?

You can see the antivent plate the only change in plane is the amount the motor runs outta water in a turn

 

[Bob_VT]

Re: No change with pitch change

Have you weighed the boat? Is there a chance you have water soaked foam?

I agree and echo the responses above .... a tach is a critical piece of the equation.

 

[steelespike]

Re: No change with pitch change

If the boat doesn't respond to trim it may have a hook in the bottom just ahead of the transom.