how wide

[nitro junky]

any suggestions on how wide i should spread the front sponsons on my scratch 21 rigger. also where should the cg be located. thanks for any help

 

[ClayGlover]

here's some plans for riggers. study them and they'll give you a good start on dimensions that have been tried already....note: you have to download the deltaCAD trial to open the files properly, the link to deltaCAD is provided. Then when you open the plans, you must use the "view" tab at the top to zoom-in to see the dimensions and such-

http://www.intlwaters.com/boatplans2.htm

 

[nitro junky]

I tried that link and didnt quite get it. I did not see anything about sponson width

 

[ClayGlover]

right click this link and click "save target as...". Then go to the downloaded file and right click, then select "open with" and click, then select "DeltaCad EXE File". Then use the scale selection's up and down arrows at the bottom of the DeltaCad screen to zoom-in and out. there are sponson dimensions listed on this one.

http://www.intlwaters.com/BoatPlans/FIRE21SST.DC

You can get DeltaCad here-

http://www.deltacad.com

 

[nitro junky]

i already have the sponson built, i need to know how wide to spread the riding surface. from outside to outside of the riding surface

 

[waterbug]

I think 14"s but don't hold me to it !!

 

[MikeP]

Here is something I found and have been using it on a couple of riggers with good results.

"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. "

I also tried to find out how wide the front sponsons should be on a .21 rigger. I found that it varys from one hull to another also owner setup.

I use propjockys formula for rigger design. Put them where they look good.

On a scratch built hull it would be good to have the front sponsons adjustable

-MikeP

 

[wswatzell]

I agree with Mike P about put them where they look good, & to make them adjustable. 1 think to keep in mind, is that the wider stance you have, the more stable it will be in the turns.

 

[ClayGlover]

Also, be sure and make provisions for turn fin movement forward and aft. A good place to start is with the trailing edge of the blade at the CG.

 

[topfuel443]

All of my scratch built riggers have been from 13-14" to the insides of the sponsons, with great results, alot depends on the rest of the design.

~ James

 

[nitro junky]

thanks for all the input guys. it has helped alot! ;D

 

[nitro junky]

what if the sponsons are like the crapshooter. I measured with the formula and it doesnt work out where it should with the type of sponson used. the CG works out to be about 3/4 in front of the engine bulhead