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  #1  
Old 08-04-2013, 03:25 PM
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Default Boat porpoise problem

I have a 1750 aluminum boat with a 40 Tohatsu and it porpoises really bad unless I have it trimed all the way down. I can lower the motor on the transom one notch. Will that help or do I need to get some trim tabs or a hydrofoil?
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Old 08-04-2013, 03:35 PM
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Lowering motor will make it porpoise more...trim tabs or a jackplate would help
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  #3  
Old 08-04-2013, 03:54 PM
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Trim tabs....hydrofoil creates drag and will slow you down.
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Old 08-04-2013, 04:01 PM
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I used to have a 50 Yamaha on a 16' Carolina Skiff. I had a heck of a time with it porposing. I installed a jack plate and fought it for months finally i I added a hydro foil and it was night and day. I could control my bow like it was on hydraulics when on plane. Made all the difference for me.
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Old 08-04-2013, 06:32 PM
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Get a rubber maul and put u a little hook in the bottom of your boat in front of the transom. Do little bit at a time until it stops bouncing when u trim it up
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Old 08-04-2013, 06:36 PM
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Quote:
Originally Posted by Top Dawg View Post
Get a rubber maul and put u a little hook in the bottom of your boat in front of the transom. Do little bit at a time until it stops bouncing when u trim it up
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Old 08-04-2013, 06:53 PM
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Trim tabs create drag also and slows you down
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Old 08-04-2013, 07:03 PM
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Cool
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Old 08-04-2013, 08:48 PM
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Adjust your load, fuel tank, battery. Something like that. Then try trimtabs but putting a hook in a boat goes against everything I have learn about boats in the last 20 years. We have knocked out hooks in hulls and and fixed the problem. I would redistribute the load first.
Do you agree Montauk17? A friend of mine said you know a little something about boats.
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Old 08-04-2013, 09:17 PM
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redistribute the load then try lowering a notch if that doesn't work. Think about it you got to trim all the way down, when you trim up the boat porpoises, you need more motor in the water to keep that from happening.
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  #11  
Old 08-04-2013, 09:31 PM
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Quote:
Originally Posted by jf522 View Post
Adjust your load, fuel tank, battery. Something like that. Then try trimtabs but putting a hook in a boat goes against everything I have learn about boats in the last 20 years. We have knocked out hooks in hulls and and fixed the problem. I would redistribute the load first.
Do you agree Montauk17? A friend of mine said you know a little something about boats.
I never heard of anybody beating a hook on the bottom. But hey,you learn something everyday. Small aluminum tabs welded on the bottom always works for me. I had a 1448 alweld with a battery and 6 gal tank in the back. Could run with two people sitting on the back without any issues with these type of tabs.

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Old 08-05-2013, 06:34 AM
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A perfectly straight bottom boat will not run above 30mph without bouncing. First step is to adjust the weight in the boat. if that doesn't stop the bounce next step depends on how much you want to spend. A lower rake prop will help, rake causes bow lift, a expensive attempt that may not work completely.
If you have never heard of a hook in the bottom of a boat, you need to look at the bottom of most hi-perf boats. We have been hooking boats for 30 years. The difference in a small hook and trim tabs is the length of the angle. Trim tabs are usually 6" long behind the boat. That small area requires a steep angle to accomplish the work. A gentle hook in the bottom starting that the back of the rear seat and ending at the transom gives you a much longer area to accomplish the same thing, no speed loss, no gathering vegetation in reverse. Like I said, been doing it for 30+ years, never slowed one down yet. Ask anyone that has purchased my hulls after I'm done with them. Ask anyone that has seen my rigs run. Better yet, here's the boat I currently own, guess what, it has a hook at the rear of the hull on the bottom. 4 stroke 40 merc with a 60 pcm in it.
I would start with a 1/8" hook and add 1/8th at a time until you can trim about 2 degrees positive with a normal load. The most I have ever hooked is 1/4". Hook only the two outside corrugations, DO NOT HOOK IT IN FRONT OF THE MOTOR!
Here's a video of the boat in the pic with the hook running black bayou:
same old 1552 WeldBilt and exact same old Merc.

Last edited by CajunChristian; 08-05-2013 at 07:08 AM.
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  #13  
Old 08-05-2013, 08:16 AM
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I stand corrected.
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Old 08-05-2013, 08:19 AM
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Quote:
Originally Posted by jf522 View Post
I stand corrected.

We're all here to learn and share I try to use the most cost effective ways to accomplish things, you know what they say "po folks got po ways".
D
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Old 08-05-2013, 08:35 AM
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CajunChristian hooked my boat. And it was night and day.
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Old 08-05-2013, 09:17 AM
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Quote:
Originally Posted by CajunChristian View Post
We're all here to learn and share I try to use the most cost effective ways to accomplish things, you know what they say "po folks got po ways".
D
In the interest of learning......

How do you "Hook" the bottom of an aluminum boat like shown in the picture holding the tap measure? I am thinking maybe using a big hammer [sledge hammer???] but think that would probably not look good after a few good hits.

Do you have to put the boat in some kind of big "press" to make the bend in the bottom?


I once tried putting a 15 hp outboard on my 12' Alumacraft boat that is rated for 8 hp max. Just me and the engine, no other weight. I don't know how fast I was going, but once that boat planed out, it felt like it was "dancing" on the smooth water. I don't remember if I tried running WOT, but for me that was too much hp for that 12' boat and did not feel safe.
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  #17  
Old 08-05-2013, 10:09 AM
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Quote:
Originally Posted by Gerald View Post
In the interest of learning......

How do you "Hook" the bottom of an aluminum boat like shown in the picture holding the tap measure? I am thinking maybe using a big hammer [sledge hammer???] but think that would probably not look good after a few good hits.

Do you have to put the boat in some kind of big "press" to make the bend in the bottom?


I once tried putting a 15 hp outboard on my 12' Alumacraft boat that is rated for 8 hp max. Just me and the engine, no other weight. I don't know how fast I was going, but once that boat planed out, it felt like it was "dancing" on the smooth water. I don't remember if I tried running WOT, but for me that was too much hp for that 12' boat and did not feel safe.
\
I use a 12" piece of 2X4 and a loaded rubber hammer. It takes much less blow than you think. I measure with a straight edge constantly to insure a smooth curvature. I usually just slide the boat back about 2' on the tail end of the trailer, lay on my back and tap away. About 10 minutes to completely hook both sides.
You want your boat to sit up on the tail and run, but, you don't want to use all available horsepower to lift the bow.
Stop this video at 2 seconds and notice the trim angle of the engine and how much boat is out of the water.
Less boat in the water=less drag. Less trim angle=less wasted horsepower. You have, let's say 50hp, how much will you use to lift the bow and how much to push forward? That is what makes our tunnel race boats so fast, air flys the boat and the motor only pushes forward.
Notice the trim angle on this race boat, and notice how much boat is out of the water:

The ways to control the bow on a loaded aluminum boat is:
weigh the bow down, not practical
trim the engine all the way down, a tremendous waste of horsepower
trim tabs, takes speed away, angle too sharp
hook the rear bottom of the hull, no speed loss
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  #18  
Old 08-05-2013, 10:39 AM
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Cajunchristian also hooked my boat and it runs great. I have welded trim tabs on my 1648 and it's like dragging a plow through the water. Way too much drag.
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  #19  
Old 08-05-2013, 11:56 AM
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To each their own....I rather weld tabs on than beat on the running surface of a boat with a hammer. On the flat I had there was no loss of speed. Took some time to get the angle right but once it was right it was all good. But I never cared to do over 30mph with a tiller steer flat anyways...
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  #20  
Old 08-05-2013, 12:05 PM
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Spunt Drag u talking about the small welded tabs like the ones that come on an Alweld or in the pic above?
I dunno if I could handle putting a hook in my brand new hull or if it would actually help, but I don't have porpoising problems either...
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