Hi guys, sorry it has taken me so long to get back with you…the Air Force has me on the road and its been kinda hard to get to the computer. It seems there is some interest in why boats hop so I will try to pass on my ideas.
Let me start off by saying that there are a lot of really good boaters with different things that work for them, so this is just my opinion based on my experiences.
Hopping is caused by an imbalance in the forces trying to make the back of the boat go up (lift) and the forces trying to make the back of the boat go down (weight). For this conversation I will not address the aerodynamics that may be applying forces (either up or down) or “bouncing” caused by improper angle/depth of the rear sponsons.
All right, here we go:
-Lift is caused by two things, 1) “style” of prop…some blade shapes have more lift than others 2) thrust angle…if the strut is set with any positive angle the “push” of the prop will have a X and a Y vector with one along the surface of the water and one perpendicular (lift).
-Each prop has a certain level it likes to ride across the water and a certain amount of power to hold it’s self at that level.
-Hop is not caused by “too much” lift…I have used all of the highest lift props on my SAW boats and they NEVER hop.
-Hop is not caused by too little tail weight…both my .21 and .12 SAW boats are pretty light (just over 2 lbs for the .21’s and now just over 1 lb for the .12) and have very light tail weight.
-What happens to make a boat hop is that the prop tries to “climb” to the level it wants to runs but the upward momentum of the boat causes it to climb higher than the prop can support (as more of the prop comes out of the water it loses the power it hold it’s self there) so the weight pushes the back of the boat back down. Now the downward momentum of the boat works to push the prop back down past the level it would like to run, and since there is now enough prop in the water to develop the necessary power, the prop pushes it’s way back up. And the cycle continues.
-On setups where the imbalance is not too bad you may have noticed that once in awhile to boat will run a short distance without hopping. This is caused by just the right water conditions and just the right application of power that lets the prop “climb” to the level it can support with out developing the momentum causing the back of the boat to “overshoot”.
-If your boat hops there are a couple of things you can do: 1) Reduce the lift on the prop so it doesn’t try to “climb” past the point it can support. This can be done by reducing the lift of the prop by cupping, cutting, changing props, etc. or by reducing the angle of the strut (I always run my strut flat). 2) Reduce the weight of the boat that is keeping the prop from running at the level it wants to get to. Yes it is possible to keep the boat from hopping by adding enough weight to completely overpower the prop lift, but you would be losing the benefit we gain with surface running props. You would be better off by getting rid of the weight and changing props.
Well, I know this is kinda long and may be a little confusing, but maybe it will help someone a little. I look forward to hear any other’s ideas…maybe we can all learn a little.
Glenn
