tunnel hull balance points ?????

[topfuel443]

hello all,

I need advice on what the balance point should be on a tunnnel hull. I have a Herb Stewart 3.5 ( 29.5" length ) im running a modified piped os outboard. Ive seen some guys writing about a certain percentage of the balance point, I took this to mean percentage of overall length from the back of the transom, is this correct? If so, im running about 28% from the transom to the balance point (about 8.5 inches).

Is there any reason why I cant or shouldnt run the irwin pipe elevated as high up and close to the engine as i can? ( this helps to get a better balance point without having to add as much weight to the front)

I will try to post a pic of it tonight if it will help.

Thanks in advance,, ~ James

 

[Grimracer]

Top

As long as you can get to the glow plug have at it. The motor will run the same.

The CG depends on a bunch things but bottom line the boat will tell you what it wants. Most MFGs have a sugejested CG and that is a good place to start. Run the boat and let it tell you what it wants. Remember it all goes out the window once you hit race water so tune with other boats on the water if you are ging to race it.

Have fun

Grimracer

 

[Flying Pilgrim]

James,

Like Grim says, you're in the right place to start. I believe the guidelines are between 27% and 30% from the transom.

F. P.

 

[Buddy Beaird]

Hi Guys!

When you are running an inset transom what point do you use to figure % point? Inset transom or stern of boat?

Thanks, Buddy.

 

[TimD]

Buddy,

I measure from the stern, as that is the end of the running surface on the water. My transom is inset by 1 inch and the balance point is at 28%

Hope this helps you out.

Tim.

 

[Jerry Dunlap]

Buddy,

Most of my boats have the motor inserted. I still measure from the back of the boat to figure the balance point. As has been stated a balance point of 1/3 the total lenght of the boat from the back running surface is a good "rule of thumb." "Rule of thumb??" is that like Murphy's Law?

In balancing a tunnel, I use stick on lead applied to the front sponson tips. Once I find the correct amount, I often insert the lead into the sponsons. If the boat is fiberglass, you can cut an access hole a couple of inches in back of the sponson tip and insert the lead into the sponson tip. I cut the lead in small chuck, mix up some epoxy and pour this mix into the sponsons. I call it "lead soup." Set the boat on its sponson tips until the epoxy cures. Take a piece of 1/16" plywood and make a cover for the access hole that extends from the back of the hole forward to the tip of the sponson.

I build a lot of tunnel out of foam and I just carve out the foam in the front of the sponson and glue the lead strips into the hull. I either smooth the area with body putty or glue on a cap piece of plywood.

Another place to stick lead is in the nose of the cowling. You can use the "lead soup" technique for that.

Jerry Dunlap

 

[topfuel443]

thanks, for all the replys ;D Just needed some reiteration on what I thought I new.

 

[Mark Anderson]

Hey Jerry heres a new trick for you. On a glass boat make your hole near the tip, put the lead and epoxy in them tape the hole over with masking tape. Then stand the boat on its nose till the epoxy dries. Then the epoxy will seal the holes as well as holding the lead in place.

If you go to the sporting goods store you can buy a bag of #8 lead shot then you just need a 1/4 inch hole to pour the lead and epoxy in.

Mark

 

[Brian Schymik]

Does anyone think there may be an advantage in putting the lead in the cockpit area instead of in the tips of the sponsons?

The reasoning behind this, is that the more weight that is put out laterally from the center of the hull, the more the boat will rock and roll. Weight in the center will make the boat automatically right itself if a sponson gets too low. Thoughts??? The amount of weight may be to little for this to really be effective, but I always put my weight in the middle anyway.

Brian

 

[Propjockey]

Good point, Brian. The only drawback is the closer to the balance point you put the weight, the more weight it takes.

The design of some hulls puts the sponson tips well ahead of the nose of the cockpit, thus requiring less weight needed to achieve balance.

I think you're right though-keeping the weight low and to the center would be best. I guess it depends on the hull.

 

[Mark Anderson]

The farther forward you put the weight the less you have to put in. Another thing to think about. When a tunnel blows off especially in a corner what does it do? Most times it lifts the left sponson and rolls into the course. So most times more weight in the left tip than the right will be beneficial. When evaluating set up changes you need to really evaluate what happened.

Mark

 

[Grimracer]

Cool Post

Mark Im with you when it comes to ballance, the further forward you place the wight the less you use.. makes sence right..

Brian, what you are doing by adding wight to the center is just that adding weight. By the way brian..adding weight to the hull is a great way to settle down a hoochie, coochie hull.. ;D

Brian you should try sticking the lead to the roof of the tunnel, right on the CG...big fun..does not get any better then that.. hummm...did i say that just now...darn i have to keep that stuff to myself. :-X

ROCK-ON

Grimracer

 

[duc]

One small disadvantage of adding weight to the sponson tips is that they will sink immediatly when one brakes loose after a hit.

Don't ask why I know that....>

 

[sjhauge]

Mike,

You need to keep your keyboard quiet ;D ;D.

BTW wouldn't that disturb the airflow by trapping more air on the CG & effectively loosen the boat ?? ???

Nameless

 

[Brian Schymik]

Mark, I agree with you on the problem of left sponson lifting in turns. But there is a different answer that I use on my sport. The plexiglass sheet that the real Budweiser hydroplane runs on the inside of the right sponson ( remember they run backwards) breaks the airflow over the top of the sponson and provides a downforce in the corner. With that, you can avoid adding unequal weight in the tips of the sponsons. I am going to add it to my tunnel this year. I saw Carl Ring run his in Florida very successfully with these over the last few years. Mike Z has them on his Villian,

too.

Mike Z. I don't know what you mean about the weight stuck on the tunnel roof. Mine has been there for 3 years. It seems fine there and it has won a bunch of races like this. Mine is right in the midline under the cockpit area. My new boat now has it in the cowling where a driver would be, just to keep the lines clean and to keep it from falling off.

Brian

 

[Grimracer]

SJH

Yea your right.. ;D

Brian...nevermind.......

Grim,stumper