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Sorry if I was unclear in anyway. My point is that would want the new floor panel to the have the strength and stiffness of the original panel or better. The reference to spanning refers to the load carrying ability of panel. The suggestions I made for the plywood or the fibreglass panel joints should be as strong as the original if properly done. Simply tabbing two panels to the center bulkhead alone for instance would not be as strong. Best of luck with the repairs.
SV Sueno, Maramu #220
Right James, I was simply responding to your earlier statement that, " (you) would look at this from the standpoint of spanning the entire distance between the two sides of the boat", which, of course, can't be done with one piece and one needs a joint.
, wrote :
There is no need to install the floor panels as one piece. If you are using plywood, just fasten and epoxy a butt block to the bottom of the joint. If you use plywood for the butt that is perhaps 25 percent thicker than the floor panel and overlap by 8x the panel thickness plus good fasteners and epoxy your jointed panel will be as strong as a full panel. If doing the solid glass panels, you can use a thinner fiberglass butt to join your panels and then scarf back the edges of each panel about 8x the thickness and glass the two pcs. Together, again as strong as a solid panel if done well. If you add any athwartships stiffeners, they could go in full length before the panels were installed which is what I will do if I go with a solid glass panel. With care perhaps I will never need to replace the original panels which are now 30 years old.
Best of luck with the pvc pipe, it should be ok if nothing extrodinary happens. I think I will either use stainless pipe or a very heavy wall fiberglass pipe with a replaceable liner.
James SV Sueno, Maramu #220
-------- Original message --------
From: "sangaris@... [amelyachtowners]" <amelyachtowners@...
Date: 11-25-2017 12:29 PM (GMT-04:00)
Subject: Re: [Amel Yacht Owners] Bow locker and hawse pipe deterioration
Thanks, again, James.
While the original floor did span the entire hull width, it was most certainly installed before the deck went on. One could not now fit a full spanning replacement piece for repair and constructing one in situ would be a bear. So, while the floor does stiffen the hull, I'm comfortable tying in two sections to the original tabbing.
Yes, it was surprising to find the original floor unfinished on the bottom - the top was gelcoated and well sealed from moisture. It was clearly the original factory installed piece. The tabbing was only on the top. Similarly, the front of the bow thruster box was also unfinished except for the corners where there's frp tabbing over the joint. This plywood is starting to delaminate and repairing it is really critical, before it totally rots out.
Finally, while the original steel pipe may have added some support to the deck, I think the vertical bulkhead between the lockers, which is tabbed into the bow thruster box is doing that work. That is, any force on the pipe would be totally transferred to the floor and thus to the vertical bulkhead and the bow thruster box. I'm comfortable with using Schedule 80 PVC pipe as the replacement and it will be bonded to the underside of the deck and the floor with the original tabbing the steel pipe had - it's only about 18" long and will be very strong in both compression and tension.
, wrote :
Thanks for the interesting discussion. 3/8” of solid glass will easily span 16” with adequate stiffness and in fact is probably overkill. On the other hand I would look at this from the standpoint of spanning the entire distance between the two sides of the boat rather than relying on the fore aft center panel and the deck to effectively support the floor. I still think that this might require a method to stiffen the floor panel some. It would be interesting to know the details of the engineering for sure but the design of the lockers and the positions of the panels suggests to me that these panels add quite a bit of strength and rigidity to the hull an deck in bow area. The center partition panel for instance I believe would see some of the windlass and forestay loads while the locker floor would stiffen the hull quite a bit. In other words, if I find the need to rebuild my forward lockers I will be sure to completely restore the original strength and stiffness and probably a bit more just to be sure that the boat has not been weakened at all.
I am surprised that the plywood forming the floor of your lockers was not glassed over even on the top side of the panel? Is there any chance that the floor had been replaced before you bought the boat? The floor on my Maramu is glassed on both sides though the glass on the bottom stops at the edge of the plywood leaving a gap at the hull since it would have been almost impossible to cover that joint from the bottom. I have seen other Maramus where the bottom of the floor panel as viewed from inside the chain locker was not glassed so it is curious as to why the construction is different. If you only have 20 square feet in the locker floor panels then the weight is certainly not going to be an issue but I think that it will be a little heavier than you thought. I am getting about 60 lbs. for the floor panel in solid glass based on your 20 square foot estimate: 20 square feet x .375 = 7.5”/12 = .625 x 96 = 60 lbs. You will also be removing the old plywood so the actual increase in weight would be less than that. For sure with the all fibreglass panels you will never have to worry about the floor rotting again.
You are correct, a 3/8” 4' x 8’ sheet of fir plywood would weigh in the neighbourhood of 36 pounds and so would a 12” x 12” x 12” block of Fir since other than the glue both of these are essentially the same thing. (grin) The 12” x 12” x 12” solid block of fibreglass would be around 96 lbs. so about 3X the density.
I do wonder if the steel pipe originally installed by Amel as the chain pipe might be needed from a structural standpoint as a compression member between the floor of the lockers and the deck in certain circumstances. An anchor launched in deep water running out fairly quickly and a ball/loop of chain jamming in the chain locker under the locker floor for instance cut put quite a bit of upward force on the locker floor. A strong compression member could carry that stress to the deck which should be quite a bit stronger than just the 3/8” fibreglass floor… Henri might have had that concern in mind when the steel pipe was specified but I am only guessing. So while I might upgrade some materials when making repairs such as using stainless pipe instead of the original steel, I personally would be a little uncomfortable reducing the strength as compared to the original design.
Best of luck with your project.
SV Suneo, Maramu #220
Thanks again, James,
Interestingly, the original construction was not fiberglassed plywood. It was just plywood with fiberglass tabbing around the edges to the hull and then finished on top with gelcoat over both the tabbing and the unfinished plywood. The underside was not finished.
I should think a thickness of about 3/8" would be sufficient since the width being spanned runs from 2-3 inches to only about 16" maximum. If I'm not mistaken 3/8 plywood is only about 1 pound per square foot, say roughly 36 pounds for a full 4' X 8' sheet (I think that's the 36 lbs you noted). In any event there's only about 20 square feet total, so the total weight will only be 25 to 30 pounds - and similar to what I removed. Plus all our stern-heavy Amels need some extra weight up front, anyway :-)
Regarding the hawse pipe support, I was able to retain the original fiberglass support structures (fillets) on the underside of the deck and on the floor by cutting and peeling out the pipe in small pieces. This will give excellent support to the new pipe akin to the original.
, wrote :
Solid fiberglass weighs in around 96 lbs. per square foot versus for instance fir plywood at 36 lbs. per square foot so it is likely that you will add some weight by going with all fibreglass panels to reach the desired stiffness but that would certainly solve the rot concerns permanently. There are bulking fabrics such as fab matt to build thickness with less weight but I have seen so many failures with those products that I would avoid them myself. I would think that you could reach the desired stiffness with a total panel thickness that was thinner than the wood plus fibreglass original so the weight increase should not be as much 3X. You could add solid fibreglass ribs to the bottom of your panels get the desired stiffness with a lighter weight as compared to a plain panel and I don’t think the ribs would interfere in anyway. If the panels in my boat rot out at some point, I would certainly consider a similar solution since the anchor locker is going to be a tough place for wood due to the ongoing humidity and dampness.
Your idea of using the conduit is interesting as it would never corrode. I wonder if it would be strong enough by itself and how to secure the ends so that it could never move? Some kind of a plastic replaceable liner inside of a heavy fibreglass pipe glassed at both ends sounds interesting and permanent.
SV Sueno, Maramu #220
Thanks, James, for your good input.
I'm thinking of using Heavy Wall Schedule 80 PVC electrical conduit for the new hawse pipe - easy to work with and should last longer than I.
May just lay up fiberglass panels for the bottoms.
, wrote :
Good information. Just note that plywood panels can definitely rot out if glassed on the top and bottom. Just think of all of the rotten plywood core decks, transoms in power boats etc. If you can however exclude the water from the wood completely or keep the moisture content of the wood below a critical level it will never rot. Epoxy resin will do a better job of excluding moisture than polyester. The edge of the plywood panel where the end grain of the wood is needs to be very well sealed since moisture will travel the fastest through the end grain. Any holes in the panel need to have a ring of epoxy around the hole to prevent any moisture entering the panel, caulking isn’t enough IMO. A Marine plywood panel should have a waterproof glue but you can buy panels that vary greatly in durability based on the wood species selected. Wood boats can last a very long time (one boat that I maintain is 109 years old and the planking is almost all original and solid) even though they remain wet for most of there lives. Using durable woods and providing good ventilation are the key points. For the bow lockers I would suggest selecting a species in the “durable” category such as Fir or Sapele. Be sure that the panel is solid core with no voids and that the inner plys are of the same species/durability rating. If the locker contains air that is saturated (near or at 100% humidity due to a lack of venting and water being in the locker) any exposed wood will tend to take on moisture and cannot ever dry. Opening the locker lids on a nice day or providing some kind of ventilation can help lower the humidity levels in the lockers and thereby extend the life of the original or replacement panels.
Thanks for the information about the chain pipe being galvanized, I did not realize this. This might be a good place for 316 stainless or perhaps using a very thick fibreglass pipe which will of course wear over time.
SV Sueno, Maramu #220
Over the years there have been several posts about the bow locker floors deteriorating due to water rotting out the plywood. I did a minor repair to mine some years ago, but other sections succumbed and I've now removed the entire floors from both lockers.