Trim tabs?

[bingman]

My 18 foot north river sled bounces when up on plane, I can trim most of it out but it still bounces a little. Weight in the bow helps a little but doesn't solve the problem. I'm wondering if anybody runs trim tabs or plates on their outboard sleds? Thanks.

[b23]

It's been my experience you get that porpoising, or bouncing, when I trim the motor or outdrive up a little to much. 

If you trim your motor back down does it help?

[bingman]

I have it trimmed almost all of the way down. I think my motor (115/85 Yamaha jet) is a little heavy for my boat which is a 18ft north river scout lite. I've noticed that on a buddies sled ( he has a wolden) there is a trim plate that sticks out a couple of inches where the jet drops down to the transom. I'm just wondering if anyone else has had this problem and if a trim plate would help.

[Alchase]

A Dolphin plate would help, but Smart Tabs are even better.

http://www.nauticusinc.com/smart_tabs.htm

[wildmanoutdoors]

So when you trim the jet all the way down does that take care of it?

My 175 outboard jet on my lite built 19 footer will also porpose when I start trimming up. I only really trim up when there is a few in the boat.

[C-Money]

Does it smooth out if you back off the throttle a little? Hope you get it figured out, when my boat starts bouncing, I am trimmed up to far.

[wildmanoutdoors]

You dont want tabs or a dolphin on a jetboat.

Here is a remedy we use. Take a piece of say 1" diameter pipe. Somthing semi thin and flexible. Stainless or aluminum. Cut 2 pieces about a foot long and slit it open longway. Now spread it open enough to slide it onto your boats bottom flange comming back off the transom.
This adds enough resistance to actually eliminate the porpoise effect.
You can trim down in length as needed. Usaully a 6 inch piece on either side is just fine.

The "trim plate" your refering to is actually a splash gaurd. It does nothing to "trim" the boat.

[b23]

I don't think a Dolphin plate would help your condition and considering you have a jet pump on your outboard, I don't know how you'd even attach it.

Any trim tab you can't remotely control is worthless.  No disrespect intended but those Smart Tabs are a joke.

[Badhabit]

Why not just bend the flange that comes off the underside the transom/hull down a few degrees? If you have a 2" flange on the bottom of the transom/hull you'll need a couple of large cresent wrenches and some 2" wide by .25 thick and about 12" long. place the steel on the top of the flange attach the cresents and then bend the flange down as uniformly as you can. Do the same to each side. You can tweak your ride that way, also level it out if it tends to run with a high side.

[b23]

Before I did anything, I'd try it with the motor trimmed down as far as it will go and make sure that wasn't my "fix" before I started adjusting or tweaking on anything else.

[wildmanoutdoors]

Why not just bend the flange that comes off the underside the transom/hull down a few degrees? If you have a 2" flange on the bottom of the transom/hull you'll need a couple of large cresent wrenches and some 2" wide by .25 thick and about 12" long. place the steel on the top of the flange attach the cresents and then bend the flange down as uniformly as you can. Do the same to each side. You can tweak your ride that way, also level it out if it tends to run with a high side.

I did not want to go there yet. Some flanges are too small. The "Pipe" trick works awesome!

[bingman]

Thanks for the input. Yes I have it trimmed all of the way down and yes it helps to throttle down but I'm not getting all of the power out of my motor if I do that. I don't have a flange that comes off of my transom, sounds like I need to weld one on.

[FC]

You aren't supposed to be trimming a jet at all, keep it all the way down to run as flat and shallow as possible. Can you run WOT with it all the way down without porpoising?

[wildmanoutdoors]

See figure 2. These sideplates are made to get more water in and lessen cavitation. They also put enough drag on to keep the boat from porpoising. This is what I have on my jet pump. Also because mine is a flatbottom I had allot of cavitation in rougher waters.

http://www.fishandboat.com/anglerboater/1999/sepoct99/jetboard.htm

I dont know your area, but Auburn Sports and marine carries them.

[bingman]

I can not. It's close at 3/4 throttle but I still can notice it a bit.

[b23]

I can not. It's close at 3/4 throttle but I still can notice it a bit.

Am understanding this correct; you can't go more than bout 3/4 throttle, no matter how far down you trim, before it starts porpoising??  Is that what you mean??? 

I'm curious, at about what speed does it start porpoising on you?  Also, you called it a sled so I'm assuming this is a flat bottom boat not a V-hull design, yes?

[bingman]

That is correct. I'm not sure on the speed. It's a scout lite, 6 degree, not totally flat.

[wildmanoutdoors]

I can not. It's close at 3/4 throttle but I still can notice it a bit.

Am understanding this correct; you can't go more than bout 3/4 throttle, no matter how far down you trim, before it starts porpoising??  Is that what you mean??? 


I'm curious, at about what speed does it start porpoising on you?  Also, you called it a sled so I'm assuming this is a flat bottom boat not a V-hull design, yes?

Barely any sleds are flatties anymore. Slight Vee's plane faster and go shallower. Also cavitate wayyyyyy less.
More surface area.

[b23]

Just goes to show, you learn something new everyday.  Cool, thank you.

[Alchase]

I missed the part of that he had a jet.

Any trim tab you can't remotely control is worthless.  No disrespect intended but those Smart Tabs are a joke.

Everyone is entitled to their opinion,
There is a whole community on the iboats forums the disagree with that statement.
That is also where I learned about them.
I have been running them on my boat for 10 years, and the made a world of difference.