Miss Geico 36 porpoise starting at low speed

[Hls1493]

My boat has stock props with 4 3s packs set to the back. With the drives at 2.5 mm up and stock props it wants to porpoise very bad In Glass water. Can?t run past about have throttle without using the rudder. When accelerating up to full speed from about 1/4 to 3/4 throttle I have to put a tiny bit of rudder it to keep it from porpoising bad. Once I hit about 3/4 throttle I can let off of the rudder and go completely straight and run wide open and it will stay planted but super wet in the front end. This is the only way and condition I can run the boat wide open. I have tried the drives lower, almost zero and moved the batteries forward and it seems to not reduce the porpoise that starts at low speed. The boat runs great in rough conditions at 2mm up. Tested 3.125 mm also and no change on glass water. I can?t even run at 1/2 throttle in glass water without major porpoise with the drives set anywhere from 2.00mm to 3.125mm up. Any ideas ?

[larryrose11]

is the hull flat? There is likely a hook in the sponsons. you should blueprint the sponsons.

https://www.youtube.com/watch?v=6SEhyXJnBYI

[Hls1493]

The furthest riding pads to the rear seem to not be very concave. Seem to be fairly flat. I can?t do the rock test on a flat surface like this guy does on this boat because on the Geico 36 the middle riding pad seems to be arched a bit. I?m assuming this is how the hull is designed, if all of the riding surfaces are supposed to be level on this hull (excluding the small steps in breaking up the sponsons) then mine is way off. I have noticed that my right side drive goes through the transom at about 2/100?s of an inch higher than the left side. I still don?t think this should cause such a problem. Has anyone else on here had to blueprint a Geico 36? I don?t want to mess up the relationship between the front and rear riding pads if this arch is by design.

[1coopgt]

You might want to have someone take a side view shot of there Gieco 36 and post it. My understanding is the Zelos and Gieco 36 use the same moulds. Could be wrong . Here's a pic of the Zelos 36 on a flat surface. The boat rests on the front sponsons and the water pickups on the rear ride pads. From the looks of it the center and rear ride pads are spaced the same amount above the flat surface.

[Fluid]

Needing to use the rudder to stop porpoising can mean that the CG is too far aft or that the props are set too high. Of course, an out-of-spec hull can also cause this.

The sponsons do not ride on the water pickups, they ride on the back edges of the steps. It appears from the photo that all the steps are very close to being at the same level. I don’t have either hull here with me to actually compare, but it would be odd to design a cat with the middle step below the others.

If a ‘glass hull is pulled from the mold too soon it can distort, this could be the OP’s problem. A difference of 0.01” in strut mount placement is small, but what matters the most is the actual depth of the props. They should be equal side to side measured on a flat surface.



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[1coopgt]

Needing to use the rudder to stop porpoising can mean that the CG is too far aft or that the props are set too high. Of course, an out-of-spec hull can also cause this.

The sponsons do not ride on the water pickups, they ride on the back edges of the steps. It appears from the photo that all the steps are very close to being at the same level. I don’t have either hull here with me to actually compare, but it would be odd to design a cat with the middle step below the others.

If a ‘glass hull is pulled from the mold too soon it can distort, this could be the OP’s problem. A difference of 0.01” in strut mount placement is small, but what matters the most is the actual depth of the props. They should be equal side to side measured on a flat surface.



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I think you misunderstood what I typed . In that picture of my Zelos the boat was resting on the front sponsons and the water pickups which are in the rear ride pads.