How to remove "hook" from bottom of boat.

[H180DSC]

Hey all,

I have been reading this forum religiously for about a year now. I am rebuilding a '76 20 foot Bayliner Admiralty. I know a lot of people say that I am wasting my time especially with it being a Bayliner, but I would rather not even discuss that aspect. The boat had a Volvo Penta sterndrive that was junk. I removed the sterndrive, sole, stringers, and transom (all rotten.......Bayliner only tabbed the stringers in, didn't seal the tops of the stingers blah blah blah. Anyway, I really like the hull design (deep vee, and closed bow), and the hull is in great shape. I have glassed in the outdrive hole with 1708 and West system epoxy and fillers, added another layer of 1708 to the entire inside of the transom, and am getting ready to laminate and install 1.5 inches of marine grade ply (yes I have explored using composites instead of ply and chosen against it). Once the new transom is glassed in, I am going to install new stringers. The factory stringers were 3/4 inch ply, and there were four of them. So here is where my questions are. 1. I want to make the two middle stringers 1.5 inches thick because I am installing an outboard bracket from Dad marine. The two center stringers will have transom knees incorporated into them. Does this sound like a good idea? 2. The rear 5 feet of the bottom of the hull has a "hook" in it, which was made worse by sitting on a trailer with rotten stringers and over 500 lbs of wet foam for a few years. What is the best way to get the bottom of the boat straight again without have to drill a bunch of holes in it? The only thing I have thought of is bolting some heavy angle or channel to the hull until the stringers are in. Any help will be greatly appreciated.

[lazeyjack]

geeze!!
Look fast powerboats need girders. , you could make up a pair, I dunno maybe 150mm deep x38mm that is two layes 19mm ply
If you could take the pattern from the inside of the boat, (there would be a hollow ) drawn out the hollow, build the girdars and glass them in this will push the hollows out(providing you made a fair girder)

[H180DSC]

lazeyjack,

Thanks for the reply. I am concerned with your idea of using the new stringer to push the hull straight. Won't that set up localized hard spots?? This would also make it impossible to have a gap between the bottom of the stringer and the boat. I don't want to introduce new problems to the project.

[rayk]

How about bracing the hull externally and using sand bags inside to push the hull out again. Stringers could be bonded in without stress. That is just off the top of my head, but I would like to see a photo to get the scale of the job.

[charmc]

Two approaches given to achieve the same end, either would work. Personally, I'd use the sandbags or cement blocks with external hull bracing. The trick is having a long enough straight edge to measure against, and your stringers will need to be "overbuilt, perhaps as much as 2" thick and as deep as possible given the deck clearance.

Just one thought: I accept that you know the limited value of such a rebuild. I'm somewhat concerned about hull integrity given what you've described. I don't know if that hull had any core. Maybe a test drill to check for soft wood inside the hull, or resin voids (as discovered by another restorer in this forum). Bottom line: you might need to build up the hull with some resin and cloth layers, in addition to new stringers.

[H180DSC]

Here are a few added points on the boat. In response to charmc, the hull is not cored. The entire hull is an alternating mat/roving layup with a thickness of 1/4" to 3/8". I should add that the "hook" (am I using the correct term...maybe warp?) is not extreme. I am powering this boat with a 115 horse 4 stroke outboard, and am concerned that any hull warp will cause drag. Am I correct in thinking that using the stringers to force the hull straight will make hard spots that will lead to stress cracks?? I have read a lot of posts on stringer installation, and the majority specify using a 1/4" gap or foam strip to set the stringers off of the hull. I really appreciate all of the help and responses that you guys provide to guys like me.

[H180DSC]

I forgot to mention, You may be wondering why I am undertaking this project on this particular boat. This build is not just for the boat. I want to learn and actually do this work on this boat for the experience. I came into this project knowing very little about boats and fiberglass work. I can not believe how much I have learned in the year since this project started. It is going to be a sllooowww process, but I get a lot of enjoyment out of doing it. I know the boat will be worth more to me when its done than anything I could go out and buy, no matter what the naysayers think. I will be posting pics of the project soon. Thanks again everyone.

[marshmat]

This build is not just for the boat. I want to learn and actually do this work on this boat for the experience. I came into this project knowing very little about boats and fiberglass work. I can not believe how much I have learned in the year since this project started.

You've hit the nail on the head. Keep this attitude up and you can do darn near anything

As for your hooked hull. I would probably go with Rayk's suggestion- block it up really solid from the outside, and weight it down inside to press the hull flat against the external bracing (use a LOT of 2x4s against the hull outside). Then get the stringer in once it's back in shape. Overbuild the stringers like crazy and brace that transom really, really well.

[H180DSC]

Here are some pics of the project. The hole in the transom was glassed from the inside using 1708 and West system epoxy. The outside of the transom is faired with West System epoxy and fairing filler. Not sure if you can see the "hook" in the bottom of the boat from the side picture.

[lazeyjack]

sorry whatever method you use that boats needs stiffening, and girdarswill do it, limber holes in girdars .
And no, there wont be hard spots

[H180DSC]

Lazeyjack,

I am assuming that when I say stringers and you say girders we are talking about the same thing. Yes I am definitely putting longitudinal stiffiners in no matter what you call them as well as lateral floors (semi bulkheads). What I was talking about with your method was that if you use the "girder" to push the hull flat, the part of the girder that is pushing on the high area will create a hard spot that will lead to fatigue and cracking (according to other posts that I have read). I guess what I need to know is: Do the stringers need a gap or foam betweem them and the hull or not. I am not trying to be dense, I just want to do this thing right so it will be safe as well as last a long time.

Thanks for taking the time to help with my questions.
Dan

[lazeyjack]

a girdar is just avery deep stringer BUT it runs parellel with the c/l Often they act as engine bearers
No prob, poeple help me with CAD and stuff, so what goes around comes around
i always used 4 in my power boats, and the sole was laid on them

[lazeyjack]

there you go, you can make em box in section or whatever, also they stffen the transom
you can download an installation dwg from Vovlo, but 600mm apart is a standard spacing for most inboards

[charmc]

Dan,

Here is a good discussion of transom, stringer, and sole work that answers some of your questions.

http://bateau2.com/content/view/144/28/

They do recommend strips of 1/4" foam between the stringers and sole to prevent hard spot damage. That makes it more important to be sure the hull has been straightened before installing the stringers. Leave the weights and outside bracing in place until the stringers with their cloth and resin coatings have cured. As lazeyjack and matt said, go ahead and overbuild those stringers, then use plenty of resin and glass cloth. What you learn from doing this project will be worth far more than a new boat. Good luck!

[PAR]

If you use stringers or other bracing against the interior of the hull, in an effort to remove some hook or hull distortion, you will develop hard spots, localized stress risers, possibly fracturing interior areas of the laminate.

Removing hull distortions is a long drawn out process. Other then cutting out the area and rebuilding it with new material, you have to resort to providing the 'glass with a new "memory".

Fiberglass is a material which has a lot of memory, meaning it will return to it's molded shape under deflection, once the strain is relieved. If a poorly fitting trailer or other problem, which has caused a distortion, has gone on for too long, the laminate will adopt the a new memory.

The easiest way to remove the hook is jacking, shimming and bracing the hull to remove it and then leaving it this way for a long time. This requires little more then time, which most folks don't have to offer. The only other way is to "relieve" the distorted area with well planed cuts (which relieves the internal stresses) in the hull, so the pieces can be braced into position, then held there with additional laminate. This is the most common method. Where to place the plunge cuts are the key and usually dependant on the shape and location of the distortion, plus what you have to do to the hull to get the transom raised back up into position.

This is much easier if the boat is in a solid cradle, on a shop floor. Overhead braces (from rafters or trusses) can lock the boat down and jacked or shimmed blocks can lift the stern to where you want it. Then the hull is cut to relieve the stresses and memory. A new laminate is applied to both sides and ground fair. Only then can the stringers and other internal supports be tabbed in. Yep, this will likely mean redoing areas of lift strakes and possible wholesale sections of bottom laminate.

If your hook isn't too severe, then you should consider just using it as is and admitting you'll not have a few MPH of possible top end. Frankly, running WOT at 35 knots compared to 38 isn't worth the trouble of fixing the bottom. You could try to use filler in the hook, to make the transition "easier" on the water flow, which will also save a lot of effort too.