aluminum boat with a rocker????

RNTbuck · Jan 5, 2011

I am working on setting up a brand new 1548 aluminum duck boat. generally we look at getting good performance out of these (35+ mph) with modded motors and jack plates and tilt trim units. this particular hull will NOT perform as many of the others just like it that i have set up. the boat porpoises badly. i have tried several different props and motor heights all with the same results. after further inspecting the hull, it has a rocker in approximately the last 20 - 24 inches of the hull and up to approximately 3/16 in some places and all the way across the hull. it appears that the rocker is caused from the last rear brace that was welded in across the floor. i do know that a HOOK of 3/16 from flat will make night and day difference, will this rocker make an equally extreme difference in the opposite direction?? the ONLY way to make this boat run and not porpoise is to run the motor with a significant amount of negative trim. when you start trimming up it starts porpoising wildly even before it gets to neutral. surely this is something i should not have to keep and live with huh?

DJ · Jan 5, 2011

Re: aluminum boat with a rocker????

RNTbuck said:
I am working on setting up a brand new 1548 aluminum duck boat. generally we look at getting good performance out of these (35+ mph) with modded motors and jack plates and tilt trim units. this particular hull will NOT perform as many of the others just like it that i have set up. the boat porpoises badly. i have tried several different props and motor heights all with the same results. after further inspecting the hull, it has a rocker in approximately the last 20 - 24 inches of the hull and up to approximately 3/16 in some places and all the way across the hull. it appears that the rocker is caused from the last rear brace that was welded in across the floor. i do know that a HOOK of 3/16 from flat will make night and day difference, will this rocker make an equally extreme difference in the opposite direction?? the ONLY way to make this boat run and not porpoise is to run the motor with a significant amount of negative trim. when you start trimming up it starts porpoising wildly even before it gets to neutral. surely this is something i should not have to keep and live with huh?

You're 100% correct. You have two choices:

1. Slow down.

2. Fix the hull.

By the way, the most powerful engine, I ever used, for Duck hunting was a Johnson 6.

idonthaveaname · Jan 5, 2011

Re: aluminum boat with a rocker????

how fast do you need to go before you catch the duck?

sorry...couldn't help myself. ;-)

99yam40 · Jan 5, 2011

Re: aluminum boat with a rocker????

Not sure what kind of modded motor you are talking about , but you may want to try a Dolfin or something like that on the lower unit to see if that would help.
I picked up a used boat that had one on the 40 hp yam, removed it and it would porpoise like that unless I moved weight to the front even when trimmed all the way down.
Put the fin back on and it runs fine , I can even trim it up far enough to get prop blow out some times without the porpoising.

RNTbuck · Jan 5, 2011

Re: aluminum boat with a rocker????

99yam40 said:
Not sure what kind of modded motor you are talking about , but you may want to try a Dolfin or something like that on the lower unit to see if that would help.
I picked up a used boat that had one on the 40 hp yam, removed it and it would porpoise like that unless I moved weight to the front even when trimmed all the way down.
Put the fin back on and it runs fine , I can even trim it up far enough to get prop blow out some times without the porpoising.

yes, i have read that also, however, wouldnt that be more like putting a band aid on the real problem (i believe there is a problem) rather than fixing the real issue at hand? i also know a bit about hooking one, however, did i mention this is a brand spanking new boat. hard to justify "fixing" a new boat wouldnt you agree?

99yam40 · Jan 5, 2011

Re: aluminum boat with a rocker????

If the boat was built that way, I am not sure what your options are at this point.
Does the jack plate give some set back and how high are you running the cavitation plate.

RNTbuck · Jan 5, 2011

Re: aluminum boat with a rocker????

99yam40 said:
If the boat was built that way, I am not sure what your options are at this point.
Does the jack plate give some set back and how high are you running the cavitation plate.

yes it was built that way. problem is, my last one which was identical didnt have it, and a buddy who also got a brand new one the same time and size as mine is not like that. i guess what im getting at is seeing if the manufacturer would make it right.

yes, the jack plate setup has a 12 inch setback and the cave plate is running approximately 3 1/2 inches higher than the bottom. exact setup ran perfect on the last hull, thats what is so puzzling and leads me to believe that there in fact may be a hull problem

5150abf · Jan 5, 2011

Re: aluminum boat with a rocker????

If there is a problem with the hull they should fix it, I don't know that it can be fixxed though as it sounds like it is welded in, but it is new and not right so it should be a warranty.

I don't doubt that that is causing the problem just suprised such a small hook could do that btu hydrodynamics are kinda funny like that.

RNTbuck · Jan 5, 2011

Re: aluminum boat with a rocker????

5150abf said:
If there is a problem with the hull they should fix it, I don't know that it can be fixxed though as it sounds like it is welded in, but it is new and not right so it should be a warranty.

I don't doubt that that is causing the problem just suprised such a small hook could do that btu hydrodynamics are kinda funny like that.

i agree with you whole heartedly, on both statements, assuming that you meant to say "rocker" instead of hook. considering what a 3/16 hook will do, im kinda not surprised i guess

by no means am i an expert, or claiming to be one, but myself and alot of my peers have seen a 3/16 hook do wonders. will make a boat that is more or less undriveable, to setting the nose and running like a champ. i will also say that my experience is also only on small (15') aluminum boats running 42mph and less

DuckHunterJon · Jan 6, 2011

Re: aluminum boat with a rocker????

What make is the boat - do they have warrantee coverage? I'd ask the manufacturer to make it right. Most likely, I'd think you would be looking at a new boat as I doubt they could do much to fix it.

As for 35 mph in a duck boat, I envy you. Mine with a 3.9 Merc will rocket right up to 5 mph. Hopefully a bit more with a new motor in the spring. For where I go, though, it's plenty. Good luck with it.

Home Cookin' · Jan 6, 2011

Re: aluminum boat with a rocker????

the first post describes a "brand new boat." Something ain't right.

Be careful out there. We have had 2 duck hunter fatalities this week in our area--both were guys falling out of small boats into the very cold water (about 37*). One guy, in his 20's, was in 4.5 feet of water. it's the "gasp reflex" that kills you when you first fall in. I now have a much deeper respect for the shallow water; until now I tended to focus on safety more around the deep water.

Heading off in a few minutes for 3 days on the marsh! Will be playing in a half dozen different boats!

mrdancer · Jan 10, 2011

Re: aluminum boat with a rocker????

As others have said, get with the mfr. to make the boat right.

If this is absolutely not possible, then you can put a hook in the hull. I've seen guys do this - flip the boat over, get a mallet and 2x4 and pound the hull in about 18 -24 inches in front of the transom. I'd do maybe 3/8-inch or 1/2-inch max, then go test it out. Maybe use your other boats to make a template to give you an idea of how much to pound in the hull.

Hooking the hull often does work to fix a bad hull, but I would only do this as a last resort.

aluminum boat with a rocker????

Cadet

DJ

Guest

Banned

Fleet Admiral

Cadet

Fleet Admiral

Cadet

Vice Admiral

Cadet

Lieutenant Junior Grade

Fleet Admiral

Petty Officer 1st Class