G3 F70 & 15 pitch prop HELP

[Jerry Bryant]

I have a G3 Aluminum 18' duck boat with a Yamaha F70 motor with a three blade prop. When turning, or attempting WOT cavitation problems prevent this from being achieved. The boat also has lift pods on the transom on starboard and port sides. When turning port or starboard the prop loses bite and rpm's have to be lessened. After 3/4 rpm's are reached prop looses bite and rpm's rise. Is this caused by the lift pods causing a loss water inducing clavation,, or are they lifting the prop out of the water as boats hull rises? It appears that the water lessens. I thought about removing each lift pod on transom and trying runs of maneuvering same pattern to see if they are causing the problem. I have never seen anything like this before on any of my bass boats. I wonder if a 4 blade prop might eliminate these problems. Would a four bladed prop address the problem I am having? I have contacted Yamaha with no response I'm sorry to say.

[brian3006]

is the boat also a tunnel hull? I have a 19 sea ark that is similar but it is a tunnel hull. It use to have the 70 on it, but now have a 90. I had similar issues when we first got the boat. On mine, I noticed that while the floatation pods are great for shallow water, they do prevent the boat from plaining out very well. they also do not allow the boat to lean in a turn. instead, the boat slides... this subjects the prop to aerated water from the boat and it would cavitate. I found that I have to keep the trim level very low to maintain stability. I also ended up having to go all the way down to a 13 pitch prop. Neither me nor the guy at the shop could believe that a 90 hp on a 19ft boat needed a 13 pitch 3 blade prop.., but the 13 gave much more thrust than the 15 and allowed the motor to finally reach the max rpm range.

I have ridden on a g3 that is similar to yours but was not a tunnel hull and the cavitation on it was borderline unusable...but the owner of this boat is hopeless to try to talk to about it when I tell him that shouldn't happen...

[99yam40]

most boats with tunnels or pockets have jack plates so you can adjust the depth of the motor to the conditions you are running .
jack it up high for straight running to get the most speed, but to turn you would need to drop it back down.
is this G3 a flat bottom or a semi V?
not only allow for depth adjustment it also sets the motor back some too

I looked around on line but cannot many pic of the back end of a G# and I am sure they make many different boats
here is a pic of one with a tunnel, but no jack plate.