Graupner Trim Tabs

[Guest]

Hello everyone, well after much searching and little advice (pity) I have managed to fix the trim tabs on the Jet Arrow. I searched and searched but all i could come up with was trim yabs on real boats so thats what i went with. Let every one know what happens soon. BUT if there's no improvement there staying "ON". Dont see the point of searching the subject out and then not doing something about it. Still enough of my rantings here are a few pics, if it helps someone then that will be a good thing. Post more when I've tested the Arrow.

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[Guest]

It will be interesting to see what effect they have. Obviously adjustable so experimentation will be needed but, to be honest I am not too sure what they are supposed to do.

From the look of them it would seem they are supposed to lift the back end and help the hull plane higher but i would have thought thtat could have been designed into the hull in the first place.

I look forward to what you think of them.

[Guest]

In the 70's I used trim tabs like these, they were used to counteract the torque from ic engines and to trim the boat for different water conditions, but later when flexible shafts came in, people used to put fix wedges under the hull to counteract torque and trimmed the fore and aft running of the boat by adjusting propellor drive angle.

SHG used to produce two types, fixed like the ones shown here, and ones that could be contolled under r/c. Maybe they still produce them. Jerome Grainger from SHG might be the man to call for a full explanation of how to use them on a fast electric boat.

By the way, used incorrectly you might find your boat runs considerably slower.

[Guest]

Thanks for the info John

you say SHG would that be

shgmodels.com who's site is currently off line at the moment but who's snail mails address is in Stafford UK?

The tabs are set at the moment flush in line with the boat. I havent had the boat in the water yet, too much wet stuff falling from the sky and having a daughter to contend with dont help either he smiles. Will post as soon as I do. If its nice tomorrow (tuesday) I'm gonna go for it.

[Guest]

Hi Steve,

Yes it is shgmodels.

Remember it is over 30 years ago since I used these things but I will try to remember how to do it.

You are correct in that you have them flush to the bottom of the hull.

Use a ruler and set them both totally flush, this is your starting point.

Now if you are using a standard rotation propellor (anti clockwise when viewed from the rear of the boat) this will try, through torque reaction, to push the starboard side (right hand when viewed from rear) down into the water, so move the trim tab on the starboard side down by say 1 turn on the turnbuckle. run the boat away from you at full power and see if it is running level side to side. You might have to trim your rudder to get it running straight (you can readjust your rudder later). You keep adjusting on the same tab until it is running flat.

That has taken care of the torque reaction, now you can adjust for nose up or down trim. On a very calm water you can run flatter, so now adjust both tabs down exactly the same amount (say 1/2 turn) to bring the bow of the boat down. You should notice that the boat will run flatter and slightly faster and run better on the chines, lifting the boat slightly out of the water.

There are other ways to get more speed as well.

One of the major ones is that if the hull is fairly thick, sharpen the chines, both side and bottom until they are 'razor edged'.

If the hull is not too thick, you can very carefully and slowly (this is a messy job) build up the rounded corners on the chines with superglue, and when set, sharpen the set glue.

Also you can polish the underside of the hull with wax, but remember that you will not be able to paint the hull until all the wax is removed.

Hope this helps you, and remember I was doing this with ic. engined boats, but I don't see any reason why it should not work with fast electric.

[Guest]

Thanks John, interesting stuff and obvious when you explain it all.

[Guest]

Thanks John for the info, Appol's for taking so long to post. The Chines ain't to bad but like all things could be better. Funny you should say about polish, I do every time she comes out of the water, have done every since I started boating, don't know why just do??????? weird maybe its something someone told me I cant remember. I havent got to the lake yet, what with one thing and another I havent had time but I really really want to just to check things out, chomping at the bit comes to mind :-). Anyways off to cook dinner (from the chippy) and again thanks 4 the info.