Okay My Super Duper Spartan problem

Outboard designs up to 14'

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Jimmy70
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Location: Bethel, NC

Okay My Super Duper Spartan problem

Post by Jimmy70 » Thu Aug 21, 2008 7:53 pm

Being I was down and out for quite sometime with sinus infection and then the flu it really punched me a good one and took along time getting my old butt back in gear, from Nov 07 to Jun 08.

So anyway I tinkered around with the boat and managed to gouge the prop into the concrete when I started the engine as the wind was blowing and that thing don't weigh much in the water and got me twisted around in the loading ramp and I thought I had enough depth, nope...Bonged it a good one, it was alum. so not much loss there. Got me a 13.5" by 19pitch SS prop and put that on and took it for a ride but it was windy so only got up to around 45mph. A few days later I took my young buddy out for a spin and let him drive it too and the prop started blowing out on us around 45mph. I had a chance to buy another SS Prop with a 20" pitch so grabbed that one and installed that. I took it over to the river on the 18th and punched it out to 52mph and again it started blowing out on me. I have the motor down to next to the last hole and that is as far as it will go down due to hitting the mounting frame. NOW IS THIS A PROBLEM BEING TO LOW??? I have had this boat up to 62mph with the old alum. prop that I dinged up so gotta be doing something stupid. I am looking for some feed back from all of you pros out there.
Jimmy

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Here is a photo from the rear. The motor is centered and sits about 1" below transom as advised.
Dreams are free, Reality cost money.

John K
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Post by John K » Fri Aug 22, 2008 5:25 am

I am no pro, but the cavitation plate looks like it is sitting about right. Does the cavitation plate stay below the water surface when the boat is running?
Last edited by John K on Sat Aug 23, 2008 5:54 am, edited 1 time in total.

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kens
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Post by kens » Fri Aug 22, 2008 1:56 pm

I am no hydro expert, but I do understand a couple of the schools on thought. One thing goes that as speed increases, then you need as little stuff in the water as possible, including props, rudders, lower units, etc. As speed goes up most of the really fast boats actually raise the motor up which has a lesser wetted area of the lower unit; they even raise it up so high that the cavitation plate is above the water.
Then there is the thought on prop-riding. As speeds get high the prop wants to climb up out of the water. My guess is that your boat is attempting to prop-ride and a standard prop will cavitate. I think try a super-cavitating prop, a surface piercing prop.

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Jimmy70
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Post by Jimmy70 » Sat Aug 23, 2008 2:48 pm

Hi All
Kens that makes a lot of sense and was my thinking too. I thought about buying one of those attachments that gives you a bigger cavitation plate but don't know if that would help or not. They don't cost that much so might be worth the money. I am also going to check on the hydro racing forum and see if they can give me some hints. I am going to try and kick the motor out one notch and give it a run and see what happens as it may not be level enough with the boat once it is on plane. I guess it is just time to tinker with things before old man winter arrives and I still got the time to do it.
Jimmy
Dreams are free, Reality cost money.

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kens
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Post by kens » Sat Aug 23, 2008 7:48 pm

No, I doubt that the Doel-Fin or whatever they call those large cavitation plates, I doubt that is the answer. At the speed you looking at, your cavitation plate is gonna dry out anyway.
Call it what you want, but at or near 60kts props want to come out of the water, 'prop-ride'; 'supercavitate'; whatever you call it.
I think you need to raise your motor up a whole lot, and get a supercavitating prop.
Then at that point you got to be careful not to killed in a blowover.

fred mcdearmid
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Post by fred mcdearmid » Mon Oct 27, 2008 2:57 pm

Jimmy, I wanted to ask you at the gathering, have you tried a 4 blade prop? I found one at West Marine that is 4 blade and has adjustable pitch. It go up or down 5 inches of pitch. the blades are also replaceable. these props cost around $150. replacement blades are $20 each. 4 blade props will cut down cavitation problems.

RoyH
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Location: Norway

Post by RoyH » Wed Oct 29, 2008 8:03 am

You need to get a cleaver prop, like a Ron Hill (Hill Marine) or something egual. I have a 16' v-bottom offshore racer with a Mercury 50Hp. I use a 11x21 Ron Hill cleaver, the propeller shaft is about 1" under the hull, and I have installed a Bobs performance waterpickup. You can make a WP yourself. I made two holes right under the water pump and installed two 10mm elbows (3/8"?), a T-fitting and some rubber hose. Remember to fit a waterpressure gauge if you lift the motor.



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Jimmy70
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Location: Bethel, NC

Post by Jimmy70 » Fri Oct 31, 2008 5:38 pm

HI RoyH
That is interesting with the cleaver prop and I would like to know if you could post a couple more shots of your water hookup for me, thanks ahead of time if you can.
Jimmy
Dreams are free, Reality cost money.

RoyH
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Location: Norway

Post by RoyH » Sat Nov 01, 2008 9:12 am

I have this boat for sale, and there is a lot of pictures in this ad:
http://www.finn.no/finn/boat/object?fin ... .svl=Bilde

This boat is built in GRP, but was originaly a plywood race-boat built by the italian Dalla-Pieta factory in the mid 60's, and raced very succesfully in offshore racing in europe. When I look at the hull I can see that it would be a lovely boat if I could have the drawings for the frames aso. Would look great in mahogny plywood 8)

Here is another picture:
Image

The waterpickup is from http://www.bobsmachine.com/

The rest is just some brass fittings and waterhose 8)

If you want to see more about how this boat type performs, here is av couple of videos, one with 90hp..
http://www.youtube.com/watch?v=BBuU4XCXZ3c

and one with 50hp (the boat apears after about 20 sec)

http://www.youtube.com/watch?v=0Z87GRit ... re=related
I'm just a starteled bunny in the headlights of life..

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