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Discussion Starter #1 (Edited)
I am curious what you guys are getting for speeds on 1872 flat bottom boats with 30" sides?

i just picked mine up and bought a 2001 Johnson 115hp 2 stroke. I am having issues with proposing around 35mph. I have raised the motor up on the highest bolt holes on the transom and the cav plate in reference to the bottom of the is about perfect. I am getting very little wash over the plate and its about 1 to 1.5" above the bottom of the boat.

The prop i am using is a Solaris 3 blade 13.25x17 and getting about 4900-5000 RPMs out of it that is WOT with the trim all the way down. I can bring it up a hair or two and its starts bouncing really bad so i get out of it. I have another prop that is kind of buggered up it was a 13.25x15 pitch but i only gained a appx 200 RPM (i think it was larger over all diameter 13.75x15) and still had issues with the porpoising.

I put a no-drill hydrofoil on that i had laying around for ****s and giggles. it just made it hard to steer and didn't help at all but the motor was also mounted lower in the water. I know a foil is a band-aid for the most part anyways.

Anyone been down this road care to share your setup?

My setup is a Alweld Flat bottom 1872 30"
2001 Johnson 115 2 stroke
24 gallon fuel cell in the back
3 trojan group 31 battery in the back
2 trojan group 31 under the front deck
it has a plywood floor and front deck currently until i can swing the purchase of my new welder.
 

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I have an 1872 SeaArk Semi-V with 28" sides. I can get about 38mph on average on calm water. In anything but calm water I tend to start porpoising also at higher speeds also
 

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Discussion Starter #3
What size motor and prop you running? Got a lot of gear in the boat?
 

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Interesting.

I have a 1872 Long Beach Custom with 31" sides, 15 gallon fuel with 115 4 stroke and 9.8 kicker on the back. It came with a 21p prop and hits the same rpm fully tucked and running 34 WOT. At that there's a slight bit of porpoise. Any up trim and it starts to jump. I've talked to a few others to get RPMs up and the plan is to go to a 17p. I've messed with the jack plate and gives little adjustment still for trim. I'm pretty sure I'll be welding on some trim tabs. I have very little front weight. 4 flange bearings. Aluminum steer stick, life jackets, 6 light housings, 2-24" light bars, ropes and gear bag. Which is nothing. With a guy up front I can get a few bumps on the trim so it's obvious weight is the key but I refuse to add weight while running and have the bow dipping while fishing...
 

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As I said in the PM my 5x4 trim tabs mostly fixed the issue but I would try to move one of the batteries up front if possible. I have two in back. My issues are pretty well gone after adding a bit to the trim tabs, never had the issues when I had more weight from extra batteries up front. Good luck
 

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I've got the same battle going on with mine, but I think the issue stems from adding poly. I'm gonna try a different prop, the one from the MotherShip, and if that doesn't correct it I know the culprit....and the cure...

There's a seldom talked about cause of porpoising, and that's what I think is causing my issues. My poly slopes down to the hull in the back, in effect creating a funky turbulence of water before it gets to the prop. It's hard to explain, but I think it has the same effect as if the back of the transom were bowed outwards, or rounded. Everything I've studied on porpoising leads me to believe boats behave best when there's a distinct, sharp line where the floor and transom meet.

I did try small homemade trim tabs and they did nothing for me, except create mad drag when I tried bending em down...

Usually it's a weight distribution issue though-too much weight in the rear of the boat.
 

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Discussion Starter #8
I would think that a 115 should push a 1872 into low 40's i guess weight plays a big factor into it. The boat drafts really shallow but i guess it being so wide/short compared to a 2072 it is not as streamlined in the water. I am gonna try moving my 3 trojan batterys out of the boat and see what difference it makes for a test run.
 

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Need to weld a 6" piece of angle aluminum (3/16 thick)at the bottom corner on each side of your transom...then take a adjustable wrench with you to the lake and slightly bend it down until it corrects the problem...and it will correct the problem...my 2082 with a 3/16 bottom,28" sides with a 150hp merc,20hp Suzuki kicker and 52 gallon fuel cell with 7 showme lights and a 3500w champion runs about 47
 
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