Powerquest_Baby!!

Ok, Ive done some testing with my boat and am wondering how do I lower my slip and increase my speed??

454 Mag carb motor--365 hp. Stock exhaust. Tested with 60 gallons of fuel and 3 people on board...2 coolers and a ton of stereo equipment! The motor has tons of power and gets on plane NO problem (even with 6+ people on board).

Right now Im turning 4600 rpm with a 23p laser 2 prop and hitting 49.8 mph GPS with a Bravo 1 1.5 gear ratio. According to the slip calculator Im at a whopping 25% slip! WHOA!!!! So either my boat weighs a billion tons (not out of the question!! Lol) or ?? Now I do have bottom paint which I know will affect my performance slightly but 5-7 mph??

Ive run some numbers on the prop slip calculator and at 18% slip I should be at 55 mph and at 15% slip I should be at 57 mph. Is there a different prop I should try or is all of this a result of the fricking bottom paint?

http://www.mercuryracing.com/propell...calculator.php

A.O. Razor

Bottom paint often creates a rough surface and adds drag, so it's not uncommon to have a higher slip with bottom paint. However, 25% is too high. Shooting for 13-15% is not a bad idea.

You need a prop with more diameter, the LaserII is a small prop, especially for a 26' single engine boat. Mirage+ 21", Revolution 4 21" are good places to start. You are also in the bottom of the RPM range for the 454MAG. The range is 4600-5000 rpms.

Powerquest_Baby!!

Ok, well I wanted to try out a 21p Mirage and a 23p Mirage plus today but couldnt get the frickin hub out of my old prop so I was only able to try one new prop...

I ran the 21p Mirage (not plus) and here are the numbers:

4800 rpm and hit a best of 55 mph gps over chop but was consistently hitting 53-54 mph. She easily gets on plane and I can feel the bow is much higher now (even with no trim) compared to the Laser 2.
I ran the numbers in the prop slip calculator and using 54 mph am now down to a nice 16% slip. Im now wondering if its even worth the hassle of trying out the 23p Mirage plus..The operating range for my motor is 4600-5000 and it seems to me that im going to drop down to at least 4400 (more cup and 2 more inches of pitch) which is too low for my motor.

bens87241

i was a having low speed and slip issue on my 241 liberator 24 foot 330hp 454 1.5 bravo drive i am running a 21 mirage and getting 42 -43 mph at 4200-4300rpm i tried a mireage plus 23 pitch expecting the rpms to come down but hoping the slip number would get better....boat now turned 3900-4000 but ran 45mph so even though it dropped rpms it gained speed. now i know every wants to run their boat in the correct rpms range to prevednt lugging and all that....but if i could lower my rpm that my motor turns but 300 rpms and gain speed i dont see that going to hurt much less rpm is less roms the big differance would be in cruising cause i dont think we all run our boat WOT all the time less rpm to go the same speed would just mean a better economy does not hurt to try to it if you have access to try one for free. Plus it all depends what you want from boat....do you just want to end speed or a balance of both. i personal know some ppl have put on a 4 blade rev 4 and took off a mirage 21 and actualy gained top end speed but 4-5 mph. So if you are happy with your performance now that is all that matters.....if you have a mind like me and want the most out of everything cause then it would be working right.....try some more If you want to just try it just to know bblades rents props for like 50 bucks 50 bucks is cheap to try to see and answer your question. But if like me if i spent 50 to try it and it worked and then i did not have the extra 450 or so to buy it, it would drive me nuts.... good luck keep us posted with results if you try another prop

Trash

The 21" Mirage is where you want to be. You might try a Mirage Plus or have it labbed. AS noted the 23 will most likely pull you down out of your RPM band. The bottom paint can slow you down a bit depending on how rough it is.

If you're really concerned about slip try a 4 blade in the 20" range and you will be pleased with it's performance. They are much smoother out of the hole, hold better and cruise better. Only down side is max speed may be down 2-3 mph over a 3 blade.

Powerquest_Baby!!

My whole goal here is top speed but I want to operate in the correct rpm range. With the 21p Mirage she is really easy to get on plane and at 54-55 mph Im happy. This isnt a speed hull but more of a wave crusher. SUPER smooth even over 3-4 foot waves. With a single big block and this hull I never expected to hit 60 mph.

Griff

Sounds like you are pretty close. The best prop will probably be a custom labbed 21 Mirage Plus. Your engine will make the most the power at 5000-5100rpms. Prop it to run 5000-5100 with a light load of fuel and 1-2 people. With a full load, you will drop a couple hundred rpms.

Wes Burmark

Beautiful boat. I like Griff's idea. Rent a labbed prop from BBlades or one of the other prop vendors. Why not shoot for 60m.p.h. with a light load of fuel and just you onboard? A little sanding/smoothing on the last few feet of the boat's bottom that will be in the water at WOT and who knows?

sprink58

I agree..in the direction you are headed with that prop ...with a slick bottom and a light load 60 is probable and realistic.

Bottom friction will make a big difference. I know I am talking different worlds here but I had a 40 Sea Ray EC with twin 3208 Cats that made 420 horsepower each at 2800 RPM. With the bottom with fresh paint the boat would top at 32 MPH...after 3 months and no scrubbing of the bottom it wouldn't make 28 MPH. I went down with a SCUBA rig and a brush for an hour and it would run 30~31.

I am pointing this out because with a planing hull...especially fast ones...bottom quality makes a difference. Now there are some theories out there that say if you get it mirror smooth it can actually slow you down but I don't think any of us will ever have that problem.

Dtile

Your x dimension looks low. Take a pic with the drive level and boat bottom and post so we can see cavitation plate and boat bottom. I use to race jet skiis, we always sanded bottom for that 1/2 mph advantage 60 gallons of fuel is 480 pds too...