center of balance question

[tick]

Hey, I'm in the process of building a 7.5cc outrigger and I have a couple of designs I'm trying to mess around with. being new to building outriggers, I'm finding it quite hard to get all the answers I need (its like a black art or something) lol. anyway, I need to know what the ideal balance point is on an outrigger, and if anyone can give me any other usefull info, it would be very much appreciated. oh yeah, and since the wallet is empty right now, I am unable to buy a motor till spring but can anyone give me a ballpark figure on how much a CMB .45 engine weighs? that way, I can make a dummy weight and do some rough estimates on where the motor mounts should go... thanks

 

[Ian Inverarity]

Tick,

A CMB CAM 45 weighs 1.2 lbs. The CG of most outriggers is between about 15% to 26% of the afterplane. The afterplane the length between the trailing edge of the riding surface of the front sponsons and the prop.

Outrigger designs are a lot more complicated than they look. A lot of experimentation and experience goes into the design. If I were you I would base your design on an existing design. But make yours very adjustable, ie make the front sponson booms adjustable and attach the rear sponsons with double sided tape. That way you can completely change the geometry of the boat by the relative angles and heights of the sponsons. You can also try other sponson designs.

Good luck!

 

[tick]

thanks, I know what you mean about being able to adjust the sponsons, I have taken that into consideration and agree that alot of experimentation will be neede before the boat will handle well and get some serious speed! I'm sure most would agree that it would be nice if someone with great experience would relase a page dedicated to working concepts of outrigger designs(pics and all)! after all, It's kind of depressing to see that I can find out how to build just about anything online, but yet the ideal outrigger design continues to remain a mystery ( to most). anyway, thanks for the info, this will prove to be most usefulll in my weeks to come!!

;D

 

[Ian Inverarity]

I have never seen a comprehensive explanantion of outrigger design, if someone has written one it has not been published that I have seen! If you have the time to look, I would recommend going back through the pages of the rcboat.com discussion group, the technical discussion section. Hidden away is a lot of little tips on outriggers and setups.

I see Glenn Quarles is on this board now, he is much more qualified to talk about outrigger design than me! ;D

Ian.

 

[MikeP]

tick,

Here is a post I copied,

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While there are some guys moving the CG forward from this, Gary Preusse told me a while back that the CG should be at about 80-85% of the "aft-hull." Measure the distance from the trailing edges of the front sponsons to the drive dog and multiply that by .825. The CG should be about that distance forward of the drive dog. The trailing edge of the turn fin should be about 1/2"-3/4" behind the CG with about 60-75% of the fin width ahead of the CG. This should make for a quick turning boat without any nasty handling habits. Almost every set-up I've seen has had the collet or square drive nut right at the CG.

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This is my own opinion.

Keep the distance from the trailing edge of the front sponsons to the prop drive dog the same as the fast boats for the size hull you are building. You should find that mounting the motor as far forward as you can and keep the weight off the transom your CG will be good.

-MikeP

 

[tick]

thats a very interesting opinion. I always thought that having to much weight up near the front would cause an object (such as a boat in this case) lean forward into a turn causing it to reduce considerably in speed....in fact i think i read this somewhere. F1 cars and most other race cars for example try to keep this from hapenning because of balance issues usually ening up in the car to loose grip on the back end and wipe out...i hope i wasn't dreaming all of this(lol). anyway, if this were true, then it not in our case cause the boat to wipe out or anything, but rather the front sponsons might start to dig in to the water. i will however try to fix the motor on in such a way that I can shift it's position as needed. I'm trying to keep the hull as narrow as possible and since the 4" shock absorbing mounts are too wide, I will try to make some custome lightened mounts that will be alittle more narrow and at the same time have multiple mounting holes for a small amount of forward/backward novement of the motor- if needed. and oh, there has been quite an interesting thread on about japanese riggres that i found most usefull!!!