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I plan on installing the bulkheads and am trying to figure out where the center of gravity of my 60 gal fuel tank shoul be. Since I am putting a 24" setback bracket with new 4stroke and 25gal transom livewell in I know it needs to be moved forward just not sure how far. If anyone can has an idea please chime in thanks.
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The CG on my boat is about 6.5' fwd of transom. That location is real obvious because the aft cross member on my EZ Loader roller trailer pivots, tilting the boat about 30 degrees when the CG passes over it. My boat is a stock Seafari with a 34 gallon tank plus 2 batteries, a 1.8 gal oil tank and a 9# anchor + 6' of chain +100' of line in the stern, and a 9# anchor on bow with 20' of chain and 300' of line in anchor locker. Motor weight is 427 lbs and bracket is a 30" Hermco; not sure of bracket weight but I'm guessing it's somewhere around 150 lbs. You could use those numbers to set up a moment balance about the current CG to solve for the CG location of the bare hull (assume it weighs about 1100 lbs). Once you have that you could then subtract the moments for the stuff you've removed and add the moments for your heavier motor, live well, gas tank, and console, etc., to figure out the new CG. I would strongly suggest using Coosa in the new transom and some sort of composite in the deck in the rear of the boat and maybe plywood in the front of the boat to make it a little less stern heavy. I'd also try to minimize setback on the bracket; Don Herman said he can make his with 18", 24" or 30" of setback. I'd also put that livewell in the front of the console, assuming there is enough room for it up in the bow of the boat! |
I am also looking to get rid of the windshield, bowrail, and bimini top that came off the seafari. if anyone is interested its yours come and get it.
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Got quite a bit of work done on the boat. Braced up the sides with some foam and glassed over the entire sides with a layer of 1708 and 2 layers of 1.5oz mat. Then added a ledger using .5 in celtec and glassed over with 2 layers of 1.5oz mat. This stiffened up the hull sides significantly! I got my custom 70gal tank built and it fits perfect. Started cutting the floor peices and bulkheads using .75in celtec and have been lookin for a nice console and leaning post/livewell. Marine connection has some nice stuff but big$$$. Might have to bit the bullet and get it.
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I'm very curious to see how that transom door turns out!
I'll be using a fishmaster t top if I can't find a deal on one locally. The fishmaster is about 1g and folds. |
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So wat do yall think of the tank? I need a livewell and dont really want a leaning post/livewell. I really wanna do a transom 20gal livewell but am now havin doubts after all the feedback from yall. Will it make a noticable difference if I put a leaning/livewell instead of a transom livewell?
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Thank u sir! I will do that. U know a good way to install the floor in sections w/o putting bulkheads in on every seam?
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The floor/stringer/hull combination on those boats forms a series of I beam boxes, very stiff. Bushwacker is the expert, but a 4 stringer 20 should not need bulkheads at all, as long as the floors are securely attached to the stringers and hull. Pretty sure my 20 Seafari had no bulkheads.
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I need them to support the floor seams and dont mind the work. I saw somewhere that they could cause hard spots and possibly cause issues? I dont know I already have em cut and laminated just havent intalled em cause I heard about the hard spot thing.
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You can put butt blocks on the unsupported joints; it's just a piece that spans underneath both sections of the sole.
Laminate to one section first and then glue with thickened epoxy when you attach the other section. Between the stringers, side stringers, and the butt joints, you should be good. |
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I would agree with Denny on putting the live well in front of the console. At least plumb it that way and give yourself options. Not an ideal place to keep bait I know, but you can`t ignore balance. |
Excellent thank u for the prompt feedback and I will keet yall posted.
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My boat will have a yeti 160 full of ice just in front of the console when im fishin so that will help a little too!
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so its strong enough without em will it be stronger with them. I already cut em and am ready to install em. I would think they would be neccessary down the center cause its quite a span! Ive already done most of the work:confused:
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the only parrallel seam is for the fuel tank hatch
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With your set up, stringers plus so many bulkheads, I don't think hull flexing will be a problem. Still, the possibility of hard spots makes it a good idea to spread the load on the hull around the base of the bulkheads, with some sort of pad. I used 4 layers of 1708 plus some thickened epoxy, some guys have used foam triangles, not sure exactly how those went together.
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I see that you're also adding a bunch of potential hard spots in the bottom at every one of those bulkheads that may cause cracks in the bottom where the relatively softer panels will tend to bend about the rigid bulkhead! The standard way of installing bulkheads is to avoid concentrated loads by inserting a trapezoidal shaped foam spacer between the hull and the bulkhead. This will allow loads from the bulkhead to spread out and gradually transition into the thinner softer panels. In his "Elements of Boat Strength" book, naval architect Dave Gerr recommends that the spacer width at the hull surface be about 8X the bulkhead width. If the spacer makes an angle of about 45 degrees with the bulkhead, it will also make it easier to lay in fiberglass tabbing between the hull and bulkhead. |
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The only bulkheads in my Seafari are the one just forward of the gas tank, and the one under the bunks, just forward of the head. Don't remember what the fuel tank bulkhead looks like, but from the attached pictures of the forward bulkhead, I'd say it's tabbed to the stringers with one layer of heavy roving. Note that there's no tabbing at all around the keel. Forum member Old Blues Player said the tabbing had come loose on his, which is why I took these pictures. Maybe his boat had a quality problem/"Monday or Friday build", but my boat has seen some very hard use on numerous Bahama trips, and those tabs still look good. You might want to install some limber holes in those bulkheads so you don't build in a bunch of water traps! Any water that gets in those spaces needs to be able to run back along the stringers where it can get to the bilge pump thru the limber holes at the back of the stringers. |
ok did some research and form what i could tell it seams if i leave an air gap between the hull laminate and bulkheads it should fix the hard spot issue. i assume this is true because the glass used to tab them in will flex with the hull :confused:. u think that would help? U cant see in the pics but i cut out the lowest corners of the bulkheads so water will drain to the bilge.
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Just a clarification. The Seafari 25 was built with one less bulkhead than it needed, plus all mine were rotted. The 4 layers of 1708 were laid on the hull under the new bulkheads and tapered so that the bulkhead load would spread. The gap between bulkhead and hull, I filled with thickened epoxy which was also wider than the bulkhead by the time it got to the hull. 3 layers of tapered 1708 to tab the bulkheads to the hull. In retrospect, I probably should have used trapezoidal foam blocks, but so far, no problems.
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The purpose of the bulkheads is to tie the stringers together to provide lateral support, which prevents them from buckling while also adding a lot of torsional stiffness to the structure. This would be particularly important if the stringers were tall thin 1x12's with a large difference between their "stiffwise" and "easywise" bending resistance. (bending about the respective horizontal and vertical axes.) However your stringers are ~2 inches wide at the top and probably 2.5-3" wide at the bottom, so they're already pretty stiff in both directions. Simply tying all 4 of them together at the top, combined with the robust tabbing of the stringers into the bottom laminate, has proven to create a very stiff and torsionally rigid structure that doesn't really need bulkheads. After thinking about the changes you've made to that hull, I've concluded that it won't have nearly as much torsional stiffness above the deck as the original Seafari had with it's cabin top and bulkhead that tied the hull sides and gunnels together, nor will it have the bending stiffness provided by the tall cockpit coaming. Therefore any extra torsional stiffness provided by the under deck bulkheads is a good thing! More robust tabbing of them to the bottom with 2 layers of 1708 would also improve torsional stiffness; taper the tabbing so top layer is a little shorter than the first one. That horizontal rib about halfway up the hull sides will make a handy shelf, but it adds virtually none of the torsional stiffness that you'd get from adding a core to the hull sides. You could maximize the overall torsional and bending stiffness of what you have at this point by building a cap with wide gunnels, a thick core, a large front deck, and a wide full transom cap. Some vertical ribs/rod holders to tie that horizontal shelf to the deck and gunnel would also add a little more bending stiffness to the hull, although it probably won't do much for torsional stiffness. |
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Wow great analogy thank you!
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Foam trapezoids here. I ripped them on a table saw. Ok, my dad, the furniture maker did. On the 25, I tabbed them in with 2 layers of 1708 in vinylester.
There is a recipe (scantling rule) for this but if you have the foam in there, it would be difficult to use too much tabbing. I wouldn't worry about using 2 layers of 1708. Getting it to stick to the vertical runs is fun.:cool: http://www.classicseacraft.com/commu...t=25405&page=9 Not trying to fit them blind, on your belly, while under the deck will be easier. :eek: |
btt...how this going?
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Slowed down for a bit and just started picking things back up. I got all the bulkheads glassed in put the floor for the fuel tank in rigging tubes for the fuel fill and vent lines and have also been preparing to core and finish the cap. I also picked up a 20' wellcraft fisherman for the console leaning post and ttop which was a steal compared to buying all the parts separately! Getting the console was big for me to move forward so should start making good progress again! I will post more pics when I get a chance.
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Here are some pics
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Are those strips of rubber you're planning to lay the gas tank on? Not a good idea as the carbon in the rubber will create a galvanic couple with the aluminum and cause galvanic corrosion of the aluminum! Better to use some thin strips of pvc board or starboard to keep the aluminum up off the tank support.
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I will be epoxy coating the tank before installing it. Will it still be an issue with the rubber?
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Should be ok IF the epoxy bonds well and stays intact. Might be worth using an etching primer and applying a couple coats of epoxy on the bottom. I painted my tank with a zinc chromate/epoxy primer from Sears when I got the boat in 1975. I pulled the tank to inspect it and replace hoses when I repowered in 2006 and it was still in good shape. But whatever you do, DON'T foam in the tank!
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