Jack plate recommedation for 4 blade prop

[ACAMACIAN]

I have a 21 ft fish and ski with a merc 225hp efi. I was running a 25 pitch tempest and decided to try a 4 blade power tech prop. With the tempest I ran 62mph at 5500 rpms. I went to a 24p on the 4 blade and dropped the rpms to 5000 and speed of 60mph. I raised the motor anout 3/4 of an inch and increased the rpms to 5200 but the speed was a little less at 58mph. With this 4 blade it feels like it is up out of the water and not plowing as much as it did with the 3 blade.
I thought by raising the motor and increasing the rpms I would go a little faster was I wrong in this thinking? Now I am not sure what to do, lower it back down or try raising it some more. Any suggestions?

Thanks

ACAMACIAN

 

[steelespike]

Re: Jack plate recommedation for 4 blade prop

Why did you go to a 4 blade?
Would be good to have more info about your boat and typical load. Also prop diameter.
While its not wrong to change models; it does introduce more variables.
Your slip with the 25 is about 16%,a little high.The 4 blade slip is 10%, more typical. 15% when raised.
I'm wondering if the motor was a little high for the 25". Lower the 25 a little at a time and see how your rpm and speed fair.
Not unusual for a 4 blade to eat up a little rpm and speed.I guess you could lower the 24" just a little at a time and see if you can
improve the slip and gain some speed. Not likely but nothing ventured nothing gained.
I think lowering the 25 is the best bet for more speed.

 

[ACAMACIAN]

Re: Jack plate recommedation for 4 blade prop

Thanks for the response. I went to a 4 blade from recommendation from a guy who had a similiar boat.I was in need of a new prop as I sort of scuffed up my tempest, not bad but some nics. I was told with my boat being that heavy the 4 blade would give me better lift, which it seems to do. Before the damage on thre tempest I tried raising and lowering and found what seemed to be the best spot.
The tepest is a 14 3/4" A40 while the power tech is 13 3/4" TRO4.
I read that the power tech ran best high in the water and that is why I raised it so much.

ACAMACIAN

 

[steelespike]

Re: Jack plate recommedation for 4 blade prop

Un fortunately I can't help much on the ss choice. Generally a 4 blade is not the choice for speed Though they do give good lift
both for holeshot and and at speed but you are dragging an extra blade.
When I was a kid I used to hang around while the adults were seting up their outboard race boats with mercs. and "surface drive" props. They used strips of wood to raise the motors 1/4" at a time It was not unusual for them to plane pretty good with one setting and fail to plane at 1/4" higher.Probably more touchy than yuour setup but I think you can see a 1/4" at a time might catch that hot speed spot.If you could run a 25" prop at 5500 and 10% slip speed could be in the upper 60s.of course as slip goes down the prop loads more so rpm will go down. You may be at the best slip/rpm/speed at 16% for that prop.
You might go to the merc site and see what their tests run for props on similar boats.
In the mean time someone may be along with more specific information.