Eastern Lobsterman 27 Listing at high speed

I have recently converted my 2004 Eastern Lobsterman 27 from a 350 270hp I/O to a bracket with twin Suzuki 200AP outboards. In perfectly flat conditions the boat will run at 41 knots planing beautifully. In any sea at all, speeds at 25knt + and the boat begins to list to one side or the other. I suspect the keel is generating lift and causing the list. I’m thing about cutting the keel off entirely or reducing its depth. Any input on this would be much appreciated.

Thanks!
Tom

 

Sorry to hear that.

You've raised the CoG a fair bit and moved it aft with your engine swap.

You could try extending the keel first before destroying it and confirm the direction you want to go.

 

Welcome to the forum.

No, the whole hull is getting too much lift. What you are experiencing is typical response when over powering a shallow V hull form (coupled with the increase of KG by moving to twin outboards). Ideally, the a hull suitable for that speed would require a deeper V to run at speed in any significant seaway. You are operating the hull outside its designed speed range.

 

It is my opinion removing the keel will make the issue worse.

Are both OBs rotating same?

 

@Tom V why do you have this desire to travel at 40 odd knots with your lobster boat?
Cruise at a speed less than 25 knots, and you will be sipping fuel (relatively), and getting good (relatively) miles per gallon - and the motion will be that much more comfortable.
If you have to undertake a long passage, what typically is the longest distance that you will be travelling?
If it is 80 miles, yes, you can get there in 2 hours at 40 knots, but it wont be very comfortable.
Or you can take an extra 2 hours, travelling at 20 knots, and be much more comfortable.

I would agree with the others above re your keel - certainly do not remove it! Much easier to try extending it first.

I would possibly be a tad concerned though about your O/B engine bracket and transom - that is a lot of weight hanging off the transom, and a significant lever creating a large bending moment, and the depth of the bracket is not much relatively - I am guessing about 16" in way of the deep boxes each side of the centreline?
Did you design and build the bracket structure, or is it a standard O/B bracket, bought 'off the shelf'?
What additional reinforcement did you add on the inside of the transom to enable it to cope with this large load hanging off it?

 

Don't be sorry, the boat handles much better, has a usable cockpit, is quiet and burns 1/2 the fuel it did before. I dont know what CoG means, yet. Thank you for reply, Tom

 

That's a good question that I don't have a good answer for. And I agree 100% with you logic.
The bracket was fabricated by weldingworldinc.com I'd call it semi custom, it was made specifically for this boat with dimensions and transom angle i provided from a stock template they build for many boats.
The bracket manufacture and the boat manufacture agreed that the transom, if in good dry condition is adequate for new loads as is. I only patched the hole. I did put in place a way to monitor any movement back there and it hasn't moved after 60 hours underway and 150-200 miles over the road. I hope i dont end up losing the whole rig and transom! Thank you for reply, Tom

 

Interesting, do you think extending the depth of keel could help? Thanks for the reply, Tom

 

I'm glad I put this out before getting out the sawzal and west system.
They are running standard and counter. They are electronic lower units that can easily switched between counter and standard. Do you think changing rotations could help? If so what would you try 1st? Thanks for the reply, Tom

 

Is it a list or does it pulse like mild Chine walk?

Lots of i/o conversions up here over the last decade and more than a few had this type of issue over the mid 20s. 5 stalls down from me is a alloy hull that was swapped to 2x 300 suzukis and did the same. I know initially they just went slow, but I'd bet the Dr that owns it had them try and find a solution. It was based loosely on a down east design as we can't really use high speed with our average sea state. Might be a few weeks but I usually bump into the Dr in the fall when hunting gets going.


I've seen everything tried, I'll be honest I've not followed up enough to know what remedy worked. It's been everything from wedges to giant tabs to stern extensions. I'll ask around next time I'm in town and see what the consensus is.

 

No, keels are nothing but a tripping hazard at the speeds you want to go, which is why you go to a deeper V hull shape at those speeds (and exactly what a deep V/deep polyconic hulls forms were designed for...speed in a seaway). Realistically, a keel only helps a shallow V hull at lower speeds or as needed to help the boat track. You are way over the design speed of that hull, so a deeper keel will not help handling at speed. If anything, a longer and shallower keel and stay out of chop if you really want to go 40+ knots.

 

What was the performance like before these mods.
In terms of speed you got and the ability to remain upright in flat calm seas and in a moderate chop sea way?

 

Tom V,

CoG is short for centre of gravity.
You've moved it up and aft with the engine swap(s).
Have you moved any weight forward?

I've experienced the same effect in a 12-passenger, aluminum i/o twin that was converted to twin o/b.
It would roll in a sea way and then just hang there, heeled over a bunch.
Eventually it would roll back but it was most disconcerting.

 

Does the boat cycle/list from side to side or just lean one way and stay on that particular side?
Do you have trim tabs on it?

 

It would stay on one side if the was no change to in the sea, wind or steering input. But the side it falls to is different depending on the above factors. It doesn’t fall to the same side every time.
Thanks