Outboard Jetboat Operation
I have been running a Wooldridge Alaskan with and outboard for the past 2 years. I run the Deshka so I am running skinny water a lot. Anyhow I hit every once in a while and even though I have the tunnel hull I still hit my foot almost every time I hit bottom. Now I am being told by a friend that I am trimming my boat wrong. I have been trying to trim it so it runs flat in the water and get more planing surface and he is telling me I should run it trimmed up to the point where the motor start to cavitate and then bump it down an inch or so. That way less of the boat is in the water and he is saying what part that is in the water it will ride higher. What is the correct way to trim it out?
This can depend on the boat, You didnt say what size wooly you have, I had a 17 foot alaskan and found it ran best w/ the foot all the way down (forward) I experimented w/ the trim while watching the GPS and found moving the foot back or up would pick up the bow some, if i went to far the boat would start to porpoise (bow up-down-up-down) you will know it when you hit that point.
The wooly I had was a 53"bottom and being a short 17 foot seemed to like the foot down and some weight in the bow (2 -16 gallon polys of fuel)
Now the new boat, which is a 20 foot, definetly likes some trim, (foot back) you can see it pick up 4-5 mph on the GPS and when you hit the sweet spot it will feel like some one let go of the anchor line.
So I suspect every boat has that spot and a GPS can be forever usefull to help find it, cavitating and backing off maybe not be the best indication of that spot.
Striking the foot on the bottom is not an indication of improper trim, mine always hit first, it was a yamaha w/ the fins on the jet and it stuck below the tunnel, so if the jet is set properly to the tunnel. It is the height of the tunnel (and they can vary) that determines how low the foot is.
I think the shorter boats w/ minimal planing surface like the foot all the way forward?? mine did.............................tell us more about yer boat.
It is a 2006 17' Alaskan with a 115/80 Suzuki 4-Stroke. I also have the wings on my foot and they are always bent up. I have to beat them back into place each winter and re-welding them.
The trimming it up until it cavitates, then bringing it back down is how I've always run a propped boat (one that's neutrally balanced). I have a 23' Wooldridge Sport Drifter with an outboard and I trim it up just enough to get it off of the hard stop at the bottom of the tilt cylinder. When the motor is resting on that, I get a "buzz" through the hull that drives me crazy. When the water is really shallow, I try too keep as much hull in the water as possible. I've noticed that it'll take less water that way. An example of that would be if you notice when you run unexpectedly over a real shallow spot at speed, your hull will level out (the bow will come down some, and the stern will lift some). I think the more hull you have in contact with the water, the larger the area the compressed water has an opportunity to act against essentially holding it off the bottom a little better and letting you run in a little more shallow water.
My boat has the tunnel as well and I can't remember hitting the foot ever. Even running over logs I don't remember catching the foot. Did Wooldridge mount your motor on the boat, or did someone else?
Using an outboard jet is not the optimal shallow water set up IMO. The outboard jet unit is a pretty succesfull attempt at making an outboard work with a jet unit. It will not work as well as an inboard given that you have a foot which has to rotate to control the boats direction. The fixed inboard intake will always be better as it doesn't have to move, plus, the IB jet has to take that water and rotate it through 90 deg with the impeller on the vertical, so less efficient than the IB with the impeller on the horizontal.
How high above the foot is the top of your tunnel? Should be flush or slightly below. To high and it'll cavitate.
I think its just the nature of the beast, if its shallow enought, the foot is going to hit, and those wings are going to get it first, but they are cheap.
Do you have a side shot of the foot set up?