BLUE GF18 by Jason

[jacquesmm]

The weight distribution is the main culprit.
The boat looks very well built, congratulations, but now let's make it run decently.
Weights:
I remember the first Cigarette 42 that we fitted with twin Merlin diesels. We had the same weight problem: we looked like Flipper the dolphin walking on his tail each we tried to get on plane. The first day, we took 5 heavy people and put them on the foredeck just to get on plane! Later we added big trim tabs and learned to play with engine trim.
In your case, I would move that console forward otherwise you will never be happy with the performance. That console looks much further back than on the plans. If you do not want to move the console, move as many weights as you can forward: tank, batteries and even put some cement blocks under the casting deck. Block them so that they don't jump and down and go through the bottom!
We counted on max. 160 lbs for the engine which is the weight of a 40 HP. (That boat will plane with a 25 an 3 persons onboard.)
Engine settings:
1" below the bottom is a little deep and may contribute to the problem. Raise it until the cavitation plate is flush with the bottom.
Trim: try to tuck the engine in, under the boat. That should push the bow down.
Last resort:
Hull wedges . . . I hate it but it will compensate somewhat for the weight.
We'll talk about that if the other solutions are not acceptable.

[Kurt]

Jaques, How about trim tabs rather than wedges ???

[jasonmcintosh]

Jacques,

That's not what I wanted to hear. What do you think of possibly putting a shim between the engine and the transom to get the engine to lean back more? Don't know if I'll do it, but wondering if it's a possibility.

I thought that I saw in the motor manual that the cavation plate should be 1.5" below the hull. Did I get this wrong? Is it better to have it right along the hull?

Moving the starting battery up is very doable. Gas tank is possible, but would really suck. Moving the console is the last thing on my list, even after dead weight.

What's a hull wedge?

Jason

[jacquesmm]

As Kurt says, trim tabs would be easier than wedges.
Wedges, shims, shingles whatever the name are like fixed trim tabs added to the hull, underneath, at the edge of the transom.
Maybe somebody can word that better . . .

A shim to trim the engine may also help but try to adjust things first.

Just for curiosity, next time you launch the boat, take sand bags with you to try different weight distributions.

[Kurt]

Jason I did a search and found a product called " Smart Tabs ". They make manual trim tabs and they come in various sizes depending on motor and boat length . They cost about $50. If your motor movement does not solve the problem you might want to experiment with these Smart Tabs to see if they solve the problem. You may have play around with them and fix their position somehow( that is why I say experiment). If they did work, I would then invest in the Bennet Trim electric tabs. (Although they don't mention it the Smart Tabs seem like they would be a problem when reversing the boat up since they are always set in a downward position.)P.S. I had the opposite problem on my PH16. My nose would not come up and the solution wound up being a Stilleto SS prop. This is after playing with the motor height a few times. Now the boat performs better than I ever imagined. I have all the confidence that your problem will be solved as well.

[jasonmcintosh]

Thanks Kurt. Those "smart tabs" seem to be around $150 and involve using pneumatic "shocks" to push down on the tab for low speeds, and allow them to come up at high speeds. I hate to spend that kind of money an have no idea whether they'll work or not.

Why did you prop make such a difference for you? I haven't tried to optimize my prop yet, but don't see why it'd contribute much to this problem.

And I'll be bringing some sand bags with me on the next outing as Jacques suggested.

Jason

[Kurt]

I thought I saw them discounted for less. In any event I would look for products similar to the smart tabs that perhaps you can experiment with. There must be ones that you can set in various positions. I am highly confident that tabs will solve your problem. When I was a kid I had a boat that would not plane off. My father welded up a pair of adjustable trim tabs and instaled them on the boat. They looked very similar to the smart tabs but you had to fix them into a set position. He gave me enough adjustment holes so that I could manualy adjust them depending how many people I took. They were crude but they solved the problem. As far a Prop's go, I found out that there are three types of SS props. There are Bow Lifters, Stern Lifters and Boat Lifters. I was initially using aluminum and I went the the SS Bow lifter. It made a big change in the attitude of boat at higher RPM's . My bow would dig down after I got over 4,500 RPM and my electric trim could not make the bow come up. With the new prop I can now trim the bow up. There are Stern Lifting props but I did not read about them and do not know if they would help in solving your problem. I would first do everything Jacques suggests since he has been there,done that and seen it all.

[Nuckingofuts]

"What do you think of possibly putting a shim between the engine and the transom to get the engine to lean back more?"

First let me say Im impressed and excited to finally see a Garvey 18 in the water. Awesome!

But.......
I agree, you have a center of gravity problem. Move EVERYTHING you can as far forward (and to port side if possible?)as you can, (tank, battery, anchor?, trolling motor). When you built the console where did, you moved the center of gravity aft. Nothing too major, but, a tradeoff.

Buy one of those adjustable jackplates (Non-hydraulic). It will both raise and push the whole motor back a bit. They arent too expensive. Also, sounds like you need to trim the motor down or in probably about as far as you can get it. If you can get an adjustable jackplate, start with the cavitation plate level with the bottom oc the hull, try it, and adjust up as needed. That along with moving your battery, tank, and whatever else you can as far forward as possible should fix the porpoising.

[gpratt]

Get on ebay and do a search for trim tabs. There were some listed that are self ajusting as you described also listed were some that you could lock into various positions via a adjustment knob. Plus the usual more expensive models.

[MadRus]

Congratulations Jason! It came out really sweet. I hope you can get the porpoising under control and get some good data on performance soon. I still like the blue.

-Dave