Hey all, been gobbling up all this great info on this site. I'm making a home made long tail with a 16hp duromax motor and a 6' shaft. I've got all the parts here or atleast ordered.

What my question is, I understand the motor to shaft angle should be around, but no more than 15 degrees, so does that mean the cavitation plate to shaft angle should also be 15 degrees?

Yes


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If possible leave some material on the end to bend up or down for fine tuning. .02

X2 ^ you will find that a little goes a long ways with adjustment. Good luck with the build!

Set your cav plate so that about 1.5-2 inches hangs past the center of the prop. Also you want about a 1/2" space between your prop and the bottom of your cav plate, with those 2 measurements plus like previously stated set at 15 degrees you will only need to measure for your length.

I just got done with a build of my own using that same motor and just took it out this past weekend for the first time. I bought backH20's cav plate kit and the motor runs on plane perfectly. Let me know if you got any more ?'s

Thanks everyone for the responses!!! What size prop did you use ptuck? I got a cheap 8.5" kkk aluminum prop. Figured if I go through one or two a year I would be happy and I tig weld aluminum so I can patch them up when they get dings. It Was hard for me to justify a 150$ stainless one when i didn't know exactly what pitch would be the best.

I used an 8x4 from backh20. It pushes my 1448 12-14mph. I got 17 going down the flint river.

Also just my opinion of those cast aluminum props, they suck! The first motor I built to take one and I cannot count how many I have broken or just wore down to nothing.

I figured I would just try a cast one for now, see what pitch works well and maby machine another shaft and buy a good prop I'd I'm not happy. I mean I could go through 8 before I break even vs 1 stainless... I agree they will probibally suck, but I don't go through much rocky areas to beat them up too quick.
Hey did you use a bushing or bearings for your lower end? I'm using sealed bearings and automotive double spring seals. I didn't know if anyone uses a system like that

Backwater will also sell you a cavitation plate to install on your frame. I'd consider that strongly. If I'm not mistaken they provide very good instruction and may even have a diagram.

No offence but I can make one nearly identical to theirs for free. I'm not saying myne will be perfect, but I'm not gonna pay 125$ for something I can make..

I just used SAE 841 Bronze bushings. They haven't failed me on my other motors yet. But i will say that when i go to a bigger motor i will buy the bearing system for backwater.

O also if you are going to build a cav plate, make yourself an adjustable bracket like Backwater. I bought there surface tracer kit for my motor and i love it.

That sounds like a very good idea. I will have to do it! Thanks for the advise!

i have been using those kkk aluminum props on my motor that i built. when i first built my motor it had a 6.5 predator on it and a 6.5 kkk prop. it did pretty good but the props wore down quickly. about a month ago i decided to upgrade to the predator 420 cc motor and had to tear the frame apart and totally rebuild it. i went with the 8.5 kkk prop that you are thinking about running. i completed my frame and got everything put back together and decided to turn the motor around to where the prop was inside the boat and lightly strap it down so i could let it run for 3 hours to break the motor in. the prop was about 2 inches above the floor of the boat and there was nothing the prop could hit. i cranked the motor and it ran for about a minute and i heard a loud pop. i walked over to the boat and my prop was gone, nut was still there. that piece of crap popped in half right down the center of the hub. luckily it all happened inside the boat and no one was hurt. i just let the motor break in without a prop. i knew these were disposable props so i did order 2. i put the new one on and did a few test runs to get the pitch on my cav plate just right. i finally got it right and decided to do a little cruising and i nicked a stump, no big deal. 20 feet later both blades came off the prop and all i was left with was a hub with no blades. luckily i still had 2 of the 6.5 props in the back of the boat so i put one on and limped back to the ramp. now after 45 dollars of props broke in less than 1 hour of run time, 1 of them never touching water, i am gonna thread me a new prop shaft and buy a real backh20 prop so i dont have to deal with cheap thai pot aluminum crap anymore.

Those props have to be made out of recycled milwaukees best cans.