Sponson weight question

[MIke J.]

I have a 7.5 prather racing tunnel that is running very good right now but it is a little hary with a slight wind blowing . Where is a good starting place to start with weight. The boat is a heavy hull. I'm running the engine height level with rear sponsons with a couple degress of trim.

 

[TimD]

Mike,

Asuming the boat is running fine when it's not windy, I would try adding weight to the Centre of Gravity (CG). That way adding wieght shouldn't upset the trim of the boat too much.

If it does not run right even when it's not windy then it is more likely to be that the CG is in the wrong spot or the trim anle is incorrect.

Hope this helps,

Tim.

 

[duc]

Hi Mike I've the accept same hull as you have.

Mine cg was not right yet. At the moment when I slamped it half throttle in a stone harbor wall it was at 26%.

I achieved this cg because I build in a lapcat I radiobox which was mounted as fas forwward as was possible. (which means it was bij 1/3 of length under the cockpit). I did not put extra weight in the hull at that moment.

One advantage I do have at the moment is that I can out weight in the pikkels now to get the cg to 28%

Where is yours at the momnet? Did you ad weight to achieve that?

I wil keep you informed about my hull

 

[MIke J.]

Sorry for the late reply. My radio box is pretty standard for that hull.(behing main canopy) My boat is apart right now as I'm working on the radio box putting in a charge jack for the receiver. I pulled the styrofoam out of the hull and noticed there was 2 lead balls in each of the front sponsons . Maybe they weigh about 3/4 of an once each. I dont know if that is stock or not as I bought the hull used. I'm going to add an extra 2oz in each sponson and see if that works.

 

[Jerry Dunlap]

I'd rather add ounces of lead to the sponson tips than negative propeller thrust angle. It has been my experience that negative prop thrust creates handling problems .

For what it's worth, there was not one single Prather tunnel hull at the 2002 NAMBA Nationals. And there were lots of tunnel hulls there. Although I didn't attend the IMPBA Internats this year, I cannot recall seeing a Prather tunnel hull at the 2000 IMPBA Internats I attended in Moline, IL.

This is an observation, not a criticism of the Prather tunnel boats.

Jerry Dunlap

 

[duc]

Hi Mike, Jerry

I've added 80 grams of lead into the pikkels. The hull is fully repaired at the moment. Tomorrow I will spray the last layer of paint on the nose. So next sunday the Union Jack will wave again on the water!

I will post the place of the cg as soon as possible and will keep you informed about the behaviour of the hull.

I would like to have another hull too but in Europe this is the only one you can get at the moment. But I guess it's not a to bad hull but the design is somewhat old.