supporting boat when working on structure?

[elioti]

Hi there, am working on a 34ft nelson( motor boat) thats in tidal waters. Am replacing all bulkheads including longitudinal ones. Are they best replaced when the tide is in? When tide is out boat sits on its sea legs putting pressure on the hull, so am concerned about the hulls shape difference when tide is in, or out. Whats the best `state` to do this in? Even if it was out of water, then it would not be in its natural shape i guess. Would guess when the tide is in is best? When tide out there seems to be pressure on hull from outside(sealegs) when tide in the hull is not pushed in so much as when out. Would be grateful of any advice. Presume is best to do when hull is at its ` widest position` so any pressure from outside will hold it together, rather than pull apart If glassed in when hull is under more pressure than its usual sea going shape? Thanks

[Kaptin-Jer]

Elioti,
My first thought would be neither, or actually, you need to replace tit for tat. Make a template of the existing bulkheads. The new bulkheads should then replace the existing with the hull in the same shape as it is now. Granted it will be easier to fit the new in slack tide, but don't glass it in until she is floating. Then the sea will help "clamp" the bulkhead in position. I think this is going to be a tricky maneuver if you are going to try to replace a 10' bullhead in one tide change. Good luck!!

[elioti]

thanks for reply. there are two longitudinal bulkheads either side of where engine will go, with small bulkheads each side, a two foot gap is between longitudinal ones. have replaced smaller bulkheads, but had do remove the longitudinal one in one go resulting in no support at one side. have glassed in the new longitudinal but not yet glassed to side bulkheads as not sure what position to do it in. When tide is in there is a 7 mm gap when tide out its closed, i think because sea leg is putting pressure on hull. Just guessing its best to do when tide is in?

picture of completed starboard side, now doing port side, can see longitudinal and side bulkheads in picture, thanks

[alan white]

I agree. The sea legs are possibly distorting the hull. So too might floating the hull be distorting the shape if the old bulkheads are not holding the shape.
What to do? Get the boat out and into a shed! Either that or take your chances. You are, after all, doing a major job that requires a lot of eye-balling and comparison of port and starboard.
Go to plan B.

Alan

[safewalrus]

What are you doing trying to carry out a major repair like that whilst the boat is in the water! Of course the boat will flex between tides and during without stiffening! Reapply / wedge in all stiffening if its not to late and get that boat out of the water as alan has said above. Sit her on her keel and use a frame to support her upright!! Don't prop her up on the sides in anyway this will cause lots of uneven 'bumps' If it's not to late that is!

Really stuffed this one up mate, should have got an expert in if your not sure, that is major work - not to be carried out lightly!! Would you have a knee operation on the kitchen table using a bread knife to open up the knee!!! Of course if the answers yes go right ahead, you'll likely get the same effect! good luck to ye, youm gonna need it!

[TeddyDiver]

Now after seen the picture inside the boat I think it's even worse than I thought before to put that perkins 6 inside..

[Pericles]

Hells teeth Elioti,

What you are doing is the equivalent of sitting on a branch, high in a tree and sitting on the wrong side of the branch as you saw it off! You must have the new bulkheads already built so as to whip one out and whip in the other.
I only hope you have not passed the point of no return.

Best of luck,

Pericles

[the1much]

Thanks guys for telling him what i wanted too,,,,,but we all know my "social" skills,,,and i didnt want him think i was,,,ummmm,,,,,well you all know,,elioti,,,,STOP!,,STEP BACK FROM YOUR BOAT,,,THEN PUT IN A CRADLE.

[Kaptin-Jer]

O.K. Guys, Walrus yelled at me, and Every one is really jumping all over this guy. I would like to hear from Elioti, because I believe that no matter how negative you all are he is going to continue. He is trying to accomplish a MAJOR refit for 0 money, or the boat would be in a cradle and we wouldn't be having this discussion. What he is trying to do can be accomplished. The boat might have a few bumps and might not be perfectly fare, but if the bulkheads are properly glassed it will hold together. Something tells me he is not too concerned with pretty, but wants safe and strong. I know you guys have more 'glass experience than I do. Lets get him through this. Let him know how to compensate for the flexing and how he has to (now) over engineer the bulkhead to hull connections. It's easy to laugh at a guy who is trying, but difficult to be creative with solutions to keep him safe.

[the1much]

its hard,,,specially with the "movement" of his "gap",,and between the movement,,which "gap" is right,,,if he waits till that 7mm gap is there,,,then glasses it in,,when the gap "goes away" SOMETHING is gonna buckle,,maybe the bulkhead,,maybe something pushing on the "inside" will push out and cause cracks,,,and the water shouldnt be that much of a brace,,cause its only pushing "in" up to the waterline,,which in theory wouldnt that push above the waterline out a little?,,,i dont think there is a SAFE way,,or a way to make the boat safe,,with all that movement.,,,,,what about it moving while the glass is kicking off?,,that will cause "bubbles" in the glass,,VERY unsafe,,,,i dont know,,,,maybe the "meds" will help,,,good luck man.

[Kaptin-Jer]

He does have a bad situation. My suggestion is to shore up what is done and tow it to a lift and spend a few hundred to put it on the hard. Just too many things happening in this condition.

[TeddyDiver]

One way to accomlish in this is to "replan" the interior. Making new bulkheads on the side of the old ones (leaving enough space between to do the work), and removing the old when new one is properly cured. Repeating this with each bulkhead after another and mission accomplished. This way it's also possible to get better placement for that massive motor..

[elioti]

Well thanks for your advice, thats what i wanted. Have been doing it as i have as have been told by different people with experience in boat building that it will be o.k., now i am begining to wonder!There is a large metal brace between the hull where a winch was once fitted, about a third of hulls lenght from the stern, then a large front bulkhead, am not replacing that! Have finished both sides and all looks well, cant see anyparts out of shape, have been told these boats( nelsons well known in uk) are heavily built and is fine what i`m doing, but of course take in what you all say? If it looks fine and nothing is coming apart, do you reckon i will be o.k. ? Hope someone can be more positive, didnt really want to tow it, lift it out then rip it all out but do want it done properly....

[the1much]

if your not getting any ripping or pushing,,,what you've done so far SHOULD be o.k.,,,,in theory,,,but i would consider how much $$ your putting IN it,,and then ask myself if all this time and $ is worth a "maybe",,,i would make a home made cradle,,at high tide, float it to ya boat,,get it under,,and wait for the tide to go out,,,then i would find all my friends with 4x4 trucks,,,and tell them you can pull more with a goat then their trucks could pull,,hehe then yank the boat up to where it wont float,,,then finish my glassing,,,,sorry for no "positive" comment,,i just dont like giving people a sense of "safety" when i REALLY dont think it would be,,or even if i have a HINT of trouble in my head.,,and as you say it seems o.k. now,,,imagine when ya get it to plane,,and them waves hitting ya,,,,the boat will flex a WHOLE lot more,,and thats when you'll know if it was safe.,,,,,,sorry man

[timgoz]

One idea might be to use threaded rod and nuts (backed by plates to distribute the load. These would brace the structure while inserting new bulkheads.

Tim

[elioti]

Have decided now, thanks to you all to take the boat out of the water! Will be putting it on a trailer and then support it by various blocks, presume this is the best way....

[elioti]

Thanks for all advice, boat is coming out of the water! Putting it on a trailer then blocking it up, guess this is better...

[Kaptin-Jer]

Go for it!!!

[the1much]

i think its 1 great decision ya made,,,good luck man ;)

[charmc]

Good decision. One definition of a good friend is one who tells you what you need to hear, rather than what you want to hear. I think you've heard from "a few good friends" here.

It was the constant change in hull support that was not good in the tidal flats, since your is not a 1 or 2 day project. Support the keel(s?) well and there will be less weight on and flexing from the other supports.

Good luck!

[Frosty]

[QUOTE=charmc; One definition of a good friend is one who tells you what you need to hear, rather than what you want to hear.
Good luck![/QUOTE]

Does'nt always work does that?

[Petros]

This is actually a similar problem they have on major aircraft structural repairs, of which I have designed many. When the aircraft is on the ground the weight of wings and engines puts loads on the center section and fuselage very different than when flying. Seldom are the large assembly jig available to hold the hull in shape when doing a structural repair. A change in the aircraft shape means serious flyablity and stablity issues at over 500 mph speeds!

The solution for field repairs is to 1) temp brace the structure as best as possible around where you are removing the part(s); 2) replace only one major part at a time, leaving as much of the adjoining structure in place as possible; 3) and then verify you are maintaining the original shape before, during and after each replaced part. If you have a stout hull, and follow this procedure, I do not think you will have any problems.

Good luck.

[Frosty]

Elliot Dont get depressed, that the last thing you need . Your doing a big job and you need interest and motivation. I don't think you have harmed anything, its not like you have took the whole deck off.

If things get wobbly brace it , thats a peice of wood with some nails, (dont hammer them right home).

You know when boats are made, most are fitted out when in the water. Theres a reason for that.

You would'nt dream of connecting a shaft to an engine out of water for instance.

When you get the boat out ,--level it up so that you can use a spirit level instead of measuring.