88/89 Oberto: Finished finally!

[glenng]

Bob, I try very hard to get my boats to balance 1/2" to 3/4" behind the sponson transoms and have had good luck with the boats launching easily and cornering well(without blowing over) so far. The CMB motors will thrive on 50% nitro. And do what Rick Sez- get rid of the angle in the strut- you do not need it pushing the nose of the boat down into the water.

 

[BobGutsell]

Hey Bob here's some piccies for you. Quite a bit less AOA than what you have.

I also weighed the boat tonight 15 pounds with fuel, used dial type bathroom scales, so could be 16 pounds, which doesn't seem too bad. Ironically, it's carrying just under 3 pound on the strut.

I'm really starting to subscribe to the idea of More power, flat strut and a prop with less lift, and a round strut.

 

[Blue Print]

Bob, What motor are you running and whats your pipe length?

 

[Hydro Junkie]

3lbs on the strut seems like a lot. Most of the boats in the Pacific Northwest are less than 1.5 at the strut, some are even less than 1lb

 

[BobGutsell]

HJ it does seem like a lot, but I don't know what I would do differently to get more weight out of the back, it's just the frames and the skins.

Merv it's a 67 greenhead, I deliberately set it at 13" to account for lack of nitro, and give me some torque to get me going with control. Methinks, I overdid it! Be rethink coming up in that department.

 

[Hydro Junkie]

I know it can be done as John Hruby's boat is less than 1.5 at the strut and he just set a NAMBA record and took home the nitro scale crown at the NATs with his 1978 Circus Circus on Saturday. I don't know his boats total weight, just that it's fast as hell, as are Kirk Maupin's Squire and Dave Brandt's Pico, the other two top scoring boats going into the final

 

[Dasboatman]

Hey Bob G.,

I had some experience with a hull built from 137 plans when I moved to Texas in 2003. One of the first boaters I met here had one completely built using Roger's plans and built stock - It just needed to be painted. The had done an absolutely beautiful job building it, and we arranged to meet at the local boat club pond - for it's maiden voyage. I'm looking for pics of what was done to the stock hull in my old computer FYI. Will post here if I find them.

• Indications were almost exactly what you are experiencing. The hull wouldn't launch, and get on top of the water. We changed everything we could at the lake site to no avail. We discussed it, and changes were made to the sponson bottoms to increase the surface area of the primary sponson ride plate.
• Next test - it would launch and get up on plane. We would start to add speed, and the boat would blow over at a relatively slow speed. I believe this was caused by the excessive amount of AOA of the hull bottom giving it a very high angle of attack, hence packing too much air underneath. We attempted to lower the strut, which reduced the sponson angle , and the boat would no longer launch so we could see if the strut depth adjustment rotated the hull and helped the blow over issue.

We were never able to make this hull a decent race boat, and it was sold. I always felt we lost a boater that would have been a very good Scale boater. His building , painting , and driving skills were well above average. I always wished we had met before he started the build, so I could have suggested changes that would yield a better hull for him. I miss my Friend in the boating community.

CHEERS !!! Bob

 

[Dasboatman]

Hey Bob G.

These were the changes made to get the hull to launch. And the spoiler was added to try to keep it on the water once we got it onto plane. We tried many different spoiler lengths. Never could reach a viable solution to the problems of this hull.

Bottom #1 pic was as built from Plan.

Sorry I don't have better news for you. Good Luck. CHEERS !!! Bob

 

[BobGutsell]

That's hilarious Bob, one of the first things I noticed when I got this framing kit was the high amount of angle in that section, seemed way more than the boat should need. Oh well, we'll keep chipping away and see what happens. I'm in touch with a few other guys who have built and raced this hull successfully, so all it not lost ......yet!

 

[Dasboatman]

Hey Bob,

I would never imply that my Friend. The additional changes I recommended to the Squire were Too much to do on such a beautifully done boat as the Squire and your Oberto. Just feel that we lost a perfectly good future Scale boater to a poorly designed hull.

Last I heard, my Friend had taken up jumping out of perfectly good aircraft to try parachuting back to Tera firma. Must have more deeply effected him than I thought - Har, Har !!!

Keep us advised, Mate. Always glad to learn something. CHEERS !!! Bob

 

[glenng]

Bob, Is that Russell Bears Squire?

 

[wayne middlemiss]

There may be a good reason for the Dumas atlas kit to have an aggressive air trap after all ??.

 

[glenng]

Dumas boats were not designed well, The sponsons were too deep and would give the boat a nose up tail down ride attitude. When you moved the strut down you did not have enough rudder in the water for the boat to turn well. I gave up on the Atlas but later built a Pay& Pak Dumas. I cut around 3/4" off the bottom of the sponsons and re-skinned them aft of the first frame. Much better but the Pay& Pak has been retired too. The Velasco hull I'm working on now has a narrower tunnel and the sponsons only extend about 15/16" below the bottom of the hull(trapping less air).

 

[BobGutsell]

Thanks to all who have offered help and Advice, I took the Oberto out this morning with the same strut, prop, & Fuel, but with pipe shortened to 12 1/2" and got her up on the plane for a couple of laps before the engine cut when I backed off to prevent a blowover. Couldn't get t to launch again after that, then realised we had a blocked needle valve, then the rudder servo went bad and that was the end of that.

Also found the curved turn fin had too much down angle on it and was pulling the right sponson down really badly.

Still have plenty to do to really sort it out, but have finally seen a glimpse of a better future, which is much more heartening. On the downside, she has a leak on the left side and picks up a lot of water in the left sponson.

Thanks again for all the help.

 

[wayne middlemiss]

Good to hear your making inroads with the big bad Bert.