How to remove "hook" from bottom of boat.

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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.:D 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)

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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.

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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.

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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.

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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;)

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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.

[lazeyjack]

Par thats good post but , he has one very weak boat, and that boat needs some stiffening no matter what
I know nothing abiut sticky stuff like fibreglass, so will leave you and Charm and a few experts to it

[jimslade]

Set the boat on three outer points. Front on the V. Back two outer strakes. Use straight 3x3 box channel steel inside an out apprx. 6 ft long,bolt together outside the inner stringers. Leave for a week. Glass new inner stringers in. Don't touch the bottom with the wood. 3 layers of glass will work. Let cure 21 days relocate steel supports to outside of outer stringers.do same for outer's. glass in holes from support bar bolts. finish and forget it. I'm not a fan of wood, your just asking for more work later.

[PAR]

You're right Lazeyjack, the laminate is pretty weak, but he knows what he has and beating him in the head about a Bayliner's scantlings, will not get anything accomplished. I too, am concerned about the conversion to a transom hung outboard (and structural requirements), but he's asking about the hook. Your practical 'glass experience makes you a very valued contributor to this and other threads.

[lazeyjack]

hey I,m not at all being facetious. i really do not know much abt glass, truly

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I'm afraid I may not have been totally clear. I do understand that this is a weak hull, and the pics I posted are with the 4 original stringers and 1/2 of the original transom removed. My plans involve a lot of hull reinforcement including thicker transom and stringers with transom knee braces (all fully encapsulated in epoxy and glass) I also plan to add at least one more layer of glass to entire inside of hull for strength (possibly 1708). I started with the question about the hook in hull, because it seems to me that I need to have the hull straight before adding anything to it. Again, this build is mostly for the learning experience, and I want to do it right. Start with poor design and improve upon it. Is this not a good way to learn all aspects of proper boat building??

[lazeyjack]

um no it is the wrong way , in my opinion,
Just a suggestion, but, would you consider builder yourself a new boat , out of ply or double diag, ?
ByTHE WAY I DONT SELL PLANS:)) I admire your tenacity, good luck mate

[charmc]

Dan,

No, I think you've been pretty clear. In your first post you said you are planning to add 1.5" plywood, glassed in to reinforce the transom, plus knees from the new stringers to the transom. Lazeyjack has focused on being sure to make the stringers extra strong, "girders" in his words, and the rest of us are just trying to get that message across of being sure to do what it takes to make the hull and transom stronger. Par has said it is best to give the hull a longer time to take the new set once you've braced it and used jacks or weights to bend it true. Sounds like good advice, also; the point, it seems, is don't force the hull into a new set with the stringers, that will just cause problems down the road. The purpose of stringers is to prevent future distortion of the hull, not to correct a current problem. So correcting the hull sag and installing new stringers are 2 separate procedures. No one is trying to beat up on you, it's just that fixing problems caused by others is sometimes harder (as you'll find out) than building a new boat, and these guys genuinely want you to succeed.

You understand it needs more than a simple fix, you're asking for advice to be sure you understand all the procedures and issues involved, and you're prepared to do the work. When you're finished, you're likely to be a pretty fair expert on boat repair, ready to help others who will be the beginners!

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Thanks to all who have contributed to this post. I have found through all of this that it is easy to misinterperet words of wisdom from intelligent builders. Sometimes I start to get a little discouraged. I just need to take this project in small steps. You guys are trying to keep me safe, and not overlook major structural components of the build. I plan to post pictures of this build as it progresses, and hopefully you guys will continue with your guidance and not get too tired of my endless questions.

Dan

[lazeyjack]

the thing is mate, when you have finished this boat, it will still be a dog, the entry is so flat and spoonshaped that it will slam badly, it is a smooth water boat You will need build a well or have the outboard on a pod, you must do what you want to do, we will all support you

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I have nothing but time on this project. I will be taking the boat off of the trailer this weekend and putting it in the garage. I will build a cradle as was previously suggested, then build bracing from from the roof trusses to slowly push the hull into shape. Not sure how long to let it set once it is pressed into shape. If I plan to add another layer of glass to the inside of the hull should this be done before or after stringer installation? Is another layer of glass necessary, and if so is one layer of 1708 sufficient? Any other suggestions for making this hull stronger besides what has been discussed?
Thanks

Dan

[jimslade]

I just looked at the pics. You should not have removed all the stringers and transom. without proper support. I would scrap the boat now. The hull can settle and twist without proper support and bunk trailers have limited use. Also glassing to support an outboard is complicated on this type of boat.

[PAR]

Dan, I think you should continue with your ideas of improving the hull structure. Though this boat isn't the best choice, it's the one you've got so see what you can do.

I don't think the hook is particularly bad, I've seen much worse, which still were in operation. The hook will develop some drag, but not enough to get excited about.

Find out how much hook you actually have. You can do this with a long straight edge and place it against the lifting strakes, bottom centerline and flat areas between the strakes. The last portion of your hull should be damn close to dead nuts flat, in the fore and aft dimension. This area is called the run and is where the boat literally sits when up on plane. Any reverse curves in this area will tend to pull the bow down (not a bad thing on some designs, even built into a few), but your boat doesn't have any "designed" hook that I know of. Place the straight edge on the transom and see how much air space is visible, which will likely be just forward of the transom. It doesn't take much hook to effect the performance of the boat, but less then a half an inch and you really shouldn't worry about it, just reinforce the hull, hang an engine and have fun. After you checked the hull, it's a lot easier to work on them, if you don't have it on a trailer and they can be better supported for wandering around the inside as you fix stuff.

The first thing I would do it get it off the trailer and on a cradle, preferably one that has wheels, if your shop is anything like mine. You can stuff it back into a corner when you're not working on it and drag it out when you've got some time to put in her. These are usually simple 2x4 affairs, cross braces, triangulated stands along the chines, keel blocking, wheels, etc. Enough to support the boat, provide a solid platform for repairs and not distort the hull further. You can hack it up, when your done and use it to build a garden bench, for the other half when you're finished or chuck it in the scrap wood pile, for your next project.

If you've decided to remove the hook, you have to plan how you'll do this. There's really only two methods, force it back into place or make relief cuts and patch the repositioned areas with more glass. The forcing method is really a judgment call, usually based on experience with how much deformation you think you can twist back into place, with minimal laminate damage (highly problematic). The cutting method means you'll literally have to reshape the affected areas under the butt of your boat, restoring the laminate in the process.

If you elect not to fix the hook, or decide to just fill the area with putty and go with it, then you're only left with fixing the stringers and transom reinforcement. The hull is weak for several reasons, but much has to do with the manufacturing method and quantity of material used. In order to get any performance out of such a burdened hull shape, these boats were built as light as practical. It saved the manufacture building costs and the light structure could be propelled with a smaller drive. In this vain, I wouldn't add additional cloth to the hull proper, but just reinforce known areas of weakness, like the stringers, transom and it's supports (conversion to outboard power). The reason is simple, the biggest performance killer in small craft is weight.

Structural considerations for the outboard conversion would include a full width bulkhead to support a splash well, some knees and tying it all together with the bottom structure (stringers, etc.). This is a bit much to describe in this format, but if you'd like to contact me, through email (click on my name), I could provide you a reasonable laminate schedule and structure upgrades, that would prevent the transom ripping off the first time you hammer the throttle, while still keeping the boat light enough to supply good performance, with the engine you intend to use.

[marshmat]

Well, Dan, it looks like you have your work cut out for you.
Pay close attention to PAR. The guy's dead right, as usual.
I'd get her off that trailer and into a well braced cradle ASAP. The hull skin alone can just barely support its own weight, it needs external support while you rebuild the stringers.
As far as the hook goes, I'd be inclined to go with the earlier idea of putting sandbags inside the hull once she's on the cradle. It probably won't eliminate the hook completely but should reduce it to a manageable level.
An outboard applies a massive force to the end of what is essentially a big lever hanging off the top of the transom. It will tend to punch the centre of the transom forward and pull the top of the transom aft. Two or three large, well-glassed knees will be needed to brace the new transom. Adding a bulkhead slightly forward of the current transom, so you can add a splash well, is a very good idea.
You're in for a challenge, Dan, but I think you'll find the experience worthwhile in the end.

[jim lee]

Removing "Hook" is -very- common with the Hot Rod Jetboat crowd. From what I've seen them do and what I read here on your post I'd go at it in this order..

Set the boat somewhere. A cradle like mentioned above sounds good. Put in the stringers and transom. Don't try to force any hook out at this point in time just glass them in like it sits.

Now, the jetboat boys flip their hulls onto a bunch of truck tires so its upside down.

rough up the gelcoat with 36 grit. You don't need to sand thrugh the color.

Measure from the transom forward 6' with a straight edge. Do a topo map of the amount of hook using a sharpie. I think it was evey 1/8" depth. (Not sure about the depth but 1/8" sounds right)

Cut glass cloth to match these shapes.

Glass them into the low spots.

Once this fires off puddy over them with your favorite marine filler.

Sand it smooth.

Coat it with your favorite undercoat. The Jetboat boys use some sort of slick teflon kinda' stuff.

flip back over and your finished.

I've seen a pro do this from start, flipping hull, to finish, back on trailer in one day. Granted, this guy had done a LOT of hulls so he knew every trick in the book. But pretty much, this is how he did it.

Hope this helps.

P.S. There is nothing wrong with doing a project just to gain knowledge. Heck that's what school's all about. Go for it!

-jim lee