Idea behind curved/angled outrigger tub at transom?

[Mike Rappold]

What is the idea behind some outrigger designs having the last several inches of the tub's bottom curved or ramped upward towards the transom - as opposed to a perfectly flat bottom tub?

Does the curved bottom work better with a single center ski over the drive shaft or more the traditional rear sponsons?

Thanks in advance.

Mike

 

[Terry Keeley]

I think it's a hangover from the hard shaft days, my SAW boat is perfectly flat and once I found the balance runs fine.

 

[Darren Sutton]

Aero- the curve at the rear helps create a negative pressure under the rear of the hull, which MAY help hold the rear of the hull down, and possibly prevent blow over. Formula one cars in the eighties had the underside curved like this. It massively increased high speed cornering ability of the chassis. It was called ground effect. To work though, on water, the sides of the tub would need a skirt to keep the air trapped underneath thus creating a vacuum. If the air spills out the side the idea doesn't work.Hope this helps.

 

[LarryConrad]

Interesting.

 

[Buckshot]

Mike,

As stated above, think of it as a aero diffuser. Helping to control lift.

And also as Terry stated, some newer riggers are flat with no after plane. I'm running one now and it works well being flat.

What cha building?

We need to play boat one of these days - if the pond recovers.

 

[anthony_marquart]

IT makes boats hard to launch.. no doubt about that. makes the back of the boat stick to the water.

 

[Mike Rappold]

I think it's a hangover from the hard shaft days, my SAW boat is perfectly flat and once I found the balance runs fine.

Terry and Buck

Are you running a single center ski or more the traditional rear sponsons mounted to the outside of the tub?

Mike

 

[Terry Keeley]

Running a single small ski on my flat bottom SAW boat but I really don't think it makes a difference, it's the relationship between the strut/rears and front end that matters.

If I was building a heat boat today it'd be flat for simplicity sake.

 

[anthony_marquart]

When you run a curved bottom, with traditional rears on the sides, you may see some of the ground effect mentioned. It COULD create a low pressure area at the rear of the tub which COULD in theory help hold down the rear of the boat.. I don't think all this really plays out much except on launch.. Just my opinion,.. I built LOTS of .12 riggers with curved bottoms because it was standard boats I had seen prior. As soon as I made a flat one it launched with half the effort.

 

[Joe Warren]

Read #8 post again. Terry hit on every aspect of the difference. Dont matter what type boat you have. Both require a different Sponson to tub set up. I find it very interesting the Little Jag 20 has 1/2 blow out on the bottom. This is a Lot of blow out for a 20 hydro & it runs very well like that.... as for FAST planing rear ski`s They seem to work best on a flat bottom boat. But I believe most I see today are too wide.....This becomes a problem in race chop..........

 

[anthony_marquart]

I think my ski is too wide,.. I have shortened as well and will be making a more narrow ones in the future. The big center ski does blast the boat up on plane but mine seems to bounce a bit in the chop.

I have heard of people having trouble with the Jag.21 launching.. just what I've heard.. and I bet that is why.

 

[Buckshot]

I think my ski is too wide,.. I have shortened as well and will be making a more narrow ones in the future. The big center ski does blast the boat up on plane but mine seems to bounce a bit in the chop.

I have heard of people having trouble with the Jag.21 launching.. just what I've heard.. and I bet that is why.

Yes the Tidewater era Jag's were finicky on launching. The current JagIII's don't have this issue what so ever.

 

[Joe Warren]

Anthony the Ski is a Quick planing surface as soon as the prop sucks the water across it you are on plane. That is what helps get the boat off the bank. many diff mfgers have used it in years pass.....