GX270 powered bathtub race boat.

Good day everyone, this is my first post.

In Nanaimo BC, on the last Sunday in july we race bathtubs.

Check it out.....
http://www.fridaydesign.com/community/nanaimo-world-championship-bathtub-race/

3 classes, stock, mod, supermod.

Typical propulsion for all classes is 8hp 2 stoke O/B's.

For this year we're building a brand new tub, powered by a Honda GX series engine. Surface drive.

Surface piercing prop question - typical prop rpm range?
Drive shaft drag an issue ? (We are about to begin fabrication of key components, so if i'm going to run the shaft in a drive tube I need to decide now.)

These are small race boats, weigh about 350lbs with pilot, make 30 mph on 8hp.

Any comments appreciated,

Team Aggressive Salmon.

 

Conceptual drawings only!!

These drawings are not to be picked apart technically, as they only represent our concept.

By all means please post comments and ideas tho....

 

http://www.fridaydesign.com/agroracer/

Check it out...

 

What the angle of the UV-joint? Have you done the calcs to make sure it will hold?

 

You are going to steer with the skeg???

 

OK all....The boat is just about there, just in time for the race! Check out some build photos at www.agroracing.com

Design has changed tons , lots of trial and error and lessons learned!

 

Photos of the GX-1 Bathtub race boat.

How does one post photos?
Think I figured it out.

 

GX-1 Race boat.

So there it is......

Custom engine mount with clutch , thrust bearing & self centering roller bearing (sealed). Custom straight shaft keyed for prop and clutch, Milled solid at ends , chromoly tube center. Shaft is tapered twice at prop end (1x for out Thai longtail props , 1x for our 15hp outboard roller bearing and seal cartridge) shaft encased in a custom shaft tube for the outboard portion, oil filled, serves as a mounting point for steering assembly. Steering by tiller for testing..to be replaced with steering wheel. Steering is triangulated for support. 2x rudders encase the prop. (prop shown is a 9" 2 blade chopper for testing only, we have 5 other race props). Rudders shown have been replaced by 3/8 alum custom ground and polished pieces. Gas tank is a modified S.S fire extinguisher(looks awesome AND holds fuel. Honda has been beefed up for marine use. Fuel pump added. Marine kill switch. Pull cord relocated over rim of tub.

 

I don't mean to be rude but that just looks like a v hull with a bath sitting on top. Hardly call that bathtub racing.

 

Hardly looks like bathtub racing!

Then you sir must not be familliar with the loyal Nanaimo bathtub society!

try to google bathtub racing. We've been doing it since 68'.

 

If you want to go as fast as possible with the limited power available, you should just use a typical flat bottom full plane hull form and keep it as light as will hold you up for the duration of the race. Your V bottom will require more power for the same speed and will be slower to climb up on plane.



This is real, though taken back in the 50's judging by the outboard, it shows about the most efficient shape you can use, when power is limited and you want to go as fast as possible. He could have removed those legs and saved a few more pounds . . .

Simply put, if I was building this puppy (I would if there was a race down here), I'd have a 1/4" plywood bottom, shaped like a clamming skiff, with just enough freeboard to keep from flooding as she jumps up on plane, with a faux tub bolted to it, much like yours. The tub would be maybe a single layer of 10 ounce cloth, possibly made by draping the fabric over a real tub and painted white. I wouldn't use an inboard, because the outboard will have better weight to HP ratio and the hard part (shaft, gearing rudder) aren't necessary. Of course I have to use a tub spicket and hot and cold handles for the controls, just because it's me.

 

I know this photo.....

BUT...remember - we race on the OCEAN! You wouldn't get out of the harbour with something like that. 7-10 ft swells eat upturned tables for lunch. Trust me on this. After 50 years of practice, we in Nanaimo (and NZ) have decided mini v's are not so bad. Also, we do run 8hp 2 stroke ob's....but they're getting hard to find these days.

 

Hey! Talk to your "frenemies" over in NZ! They know what's up.....

 

Hey PAR.....Check out www.agroracing.com (our current site).Has not been updated in sometime) And remember we are straight shaft. No turning the power 90 deg, no reduction, no gear case obstruction, simple.

Build photos show our "step", planning surface....it's a 1 1/4" depression that receives a variety of "planning surfaces". These are bolt on and interchangeable for different race-day conditions.

 

BTW....
The tub is 2x 6 oz and epoxy, hull 2 6 oz , 17 oz roving....Nitex strips in spray rails before roving, then foam inserts then another Nitex .... while layup is wet (still) we attach the 2x 6 oz tub to hull....17 oz roving inside tub to join as one chemical unit. Deck was added later. (6 oz / roving / 6 oz). LOng, hot layup with west system and the 206 hardener for slow.