Airborne gas scale hydro


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scott williamson

Well-Known Member
Nov 14, 2010
Hi all, i just ran my new gas scale hydro last weekend for the first time and although i was happy with the speed ,i need to do something about keeping it on the water. it was a very windy day with a lot of boats blowing over but i also ran my shovelnose gas scale (which also flipped) but was generally more stable.Both hulls ive built from fibreglass scaling up from Newtons plans .The shovel is the 72 Miss Timex with a short airtap behind the sponsons .The new boat is the 73 Budweiser, plan No 108 with a full length airtrap tapering to the back.I thought the hull might trap too much air when i was building it but i wanted to keep it scale. The balance point is about 2 inches behind the sponsons ,ive kept the weight as far forward as possible.The Miss Timex weighs 21 pounds and the Miss Bud feels about 2 pounds lighter,it accelerates harder and turns a lot sharper but the sponsons would bounce on the chop at half throttle heading into the wind.On the last run i emptied the tool box into the front of the boat which helped keep it down,but would prefer not to add weight .I adjusted the strut depth a few times keeping the prop 6717 angled down.The only thing missing from the boat is the dummy merlin engine cover which seems to help keep the front down on the shovelnose.Im not sure if i should reduce the airtrap after the sponsons ? or modify the tunnel depth ? or just add more weight. Any advice is greatly appreciated. Thanks scott.

miss bud gas scale vs 22 001.jpg
You should drop the struts and add some angle to get the ride ok. Balance point should be at or near the front sponson backs. The hulls as drawn do have more angle on the belly than needed. A flatter bottom up to the front sponsons would help too.

Strut adjustment and added nose weight will trim the boat out.

Speedmaster makes a longer strut for cats that work best on the big gas hydros.
I would suggest measuring the sponson depth, then make sure that the strut depth is at the same depth of the sponsons at the back of the strut. Measure to the center of the shaft/stut. Put about 7 degrees angle in the strut. It won't hurt if the strut is a little deeper than the sponsons, but if it's higher that will definately make the boat more prone to blow over. Experiment with some 3 blade props, they tend to roll the nose of the boat over which will help. Adding weight to the nose will help as well, but I would try the other things first. See what happens.
Yea i found that when i setup my boat last year I set the strut at the sponson depth, but they needed more depth, about 1/2 inch more. thats when I got the deeper struts from Speedmaster. My T boat or Scale dont need extra weight,,, yet.
Thanks guys ,i did start with the center of the prop at sponson depth,then dropped it further which just made the nose run too hard on the water,i will try more strut variations and props next time. The engine position is the same distance from the transom on both boats ,being the full length of an off the shelf flex shaft ,the Miss Timex has a shorter afterplane though.I may move the engine forward and get a longer shaft.