This Electric Stuff Is FUN!

[Propjockey]

[SIZE=12pt]HELP![/SIZE]

Ok...here we go! I refitted the stuffing tube out the bottom of the transom, extended it three inches and installed the Kyosho Mega...HUGE difference! I went with a smaller prop and again got a big increase in speed...BUT, now it porpoises like mad.

I raised the prop to null out the porpoising until it cavitates so bad the speed drops off. There's no happy medium...it either porpoises or cavitates. ???

The best angle on the shaft seems to be about 4 degrees down.

What should I try next? Trim tabs?

 

[Finne]

that's odd I think.

where is the CG of the boat now?

 

[Propjockey]

The hull is exactly 21.5".

The balance point is 6.5" -- just a hair over 30%.

Anyone have an idea?

 

[Don Templeton]

P J,

I had a small electric Deep -V at one time with the same problems. Trim tabs really helped out but I had to play with them a little to get them right.

Don

 

[LOU]

Try 2 pieces of .020 thou clear lexan and use good carpet tape to fasten them to the bottom center of the hull at the transom edge. Make the peices about 1/4 inch wide and 1 inch long.

I'd try this before trim tabs. I hate trim :-X tabs

LOU

 

[Finne]

um... do what?

Never heard of that before. What effect will it have on the boat?

 

[LOU]

It will keep the front end of the boat down.

LOU

 

[AValentine]

...and create drag? That will definitely keep the nose down, but canwill make it run to wet and lose speed.

Get some light aluminum and make your own tabs. I've had similar problems on a few hulls. Tabs, even set neutral elliminated the problem. The first thing I'd check however, is the bottom edge of the transom sharp or rounded? I've used some tape along the edge and filled it with CA. Once it's dry, pull the tape and sand the edge nice and sharp.

 

[forresterace]

Trim tabs set at neutral, effectively lengthen the hull and therefore have a similar effect as moving the CG forward.

 

[LOU]

but canwill make it run to wet and lose speed.

Sorry Andy. I ment to say .020 thou. It doesn't create that much drag. I'm not saying trim tabs are no good. I just don't like having that variable to screw up while im racing. Iv'e got 2 boats with this setup and it works good. It's a quick, cheap fix but they can come off. Squaring the transom and making sure the back edge is the highest point is allways a good idea.

LOU

 

[Propjockey]

Thanks guys. The transom edge is rounded, so I'll start by sharpening it. If that don't get it, I'll whip up some tabs. What size?

 

[AValentine]

Trim tabs set at neutral, effectively lengthen the hull and therefore have a similar effect as moving the CG forward.

If the tabs are in the water while on plane... After that they can help the boat "fly" and keep the air under control. On my LS Offshore boat I have the inside edge of the tabs cut at a angle. More tab in the water at lower speeds, very little if any in the water while on plane and smooth water.

 

[AValentine]

Thanks guys. The transom edge is rounded, so I'll start by sharpening it. If that don't get it, I'll whip up some tabs. What size?

22" boat? How wide is it (beam)? The nice thing about making your own is that you can experiment, and reshape them until you find the right size. Start with something like 1 1/4-1/2" wide and 1-1 1/4" long. You may be able to start with servo tape to mount them, then when you know how wide they will be you can make them permenant with a couple 4-40 SS bolts.

When mounting them, center them between the keel and chine. Use a straight edge on the hull bottom to make sure the tab is flush or slightly above the transoms bottom edge. Don't want to create any drag!

 

[Propjockey]

Beam is 7-1/2" at transom, and tapers quickly after that. I sharpened the transom bottom edge with epoxy (sanded) and that fixed about 75% of the problem.

I think trim tabs are still in order, but I don't think they will have to be very large to get the desired results.

Thanks everyone.

Pete...you ready to race?

 

[Propjockey]

Well...I think that's about the best I'm going to get out of this 'el-cheapo' boat, but I'm happy with the performance/cost ratio.

Run time is about 6 minutes.

Trim tabs are 1-1/4" wide at the transom, with the inside edge angled so the trailing edge is 1".

5/8" long.

I'll throw some paint on it and get some pics up.

 

[LOU]

Race? Did you say Race ;D

More pis and Video here http://www.lousfastrc.com/PspecOffshore.html

I'm racing 4 min on an offshore course with 2400's and Winning. It can't cause that much drag.

LOU