77 hunter hull dimple???? - SailNet Community

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  #1  
Old 01-12-2006
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77 hunter hull dimple????

I''m a recent boat owner and am slowly learning by the good graces of others, with that said I have no idea why or what to do about the fact that on both port and starboard sides 2 feet below the aft chainplates there are concave dimples on the outer hull. 1 the size of a pie plate the other is about 6 inches. There doesn''t appear to be any cracking, has anyone seen this before???
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Old 01-12-2006
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77 hunter hull dimple????

This is a difficult question to answer without actually seeing the boat. Hunters of that era were actually pretty well built, but they were high production value oriented boats. The dimples can result from a lot of sources some benign, some not so benign. Dimples like that can occur from bonding the internal chainplate attachment before the hull has properly cured. As the resin continues to cure it shrinks and creates a dimple. This is actually quite common in boats of that era. Anther relatively benign cause might be a chainplate that was not properly bent to the curve of the hull or which was overtightened on installation.

On the other hand this may be the result of a separated knee, hull delamination, overtightened shouds, or improper engineering of that particular model. These are less benign.

You probably ought to see if you can a marine surveyor or experienced boat repair yard to take a look.

Good luck,
Jeff
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Old 01-15-2006
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77 hunter hull dimple????

I agree with the previous post, I''d say to take a good look at the deack above the dimples to see if there is a corresponding hump, may be hard to tell if there''s any deck camber If there''s no hump, look under the deck to see how the knees are installed, look above them to see if there is a plywood ''plate'' or some way to reinforce the top area by spreading the load over a larger area, look to see if it''s ''flat'' or bent/crushed by the knees may be able to bed some plywood under the decksides and give the knee a better surface to press against. best is to fill the area above the ''plate'' with something so it''s able to use the whole structure for strength. Knees only work by having an upper surface to press against, If the original surface or the knees have failed for some reason maybe water intrusion, (we are talking chainplates here!) the knees will be able to torque upwards, creating the dimples.

also, check tension on the shrouds, may be too high, which will also cause the same issue on lighter hulled boats, normally comes with the humps.

ken.
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Old 01-18-2006
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77 hunter hull dimple????

thanks for the info,
I have since checked and released shroud tension, which wasn''t extreme, checked the knees wich are in good condition tight to the hull. No apparent humps on deck or below.
In my search someone suggested this could be a manufacturing issue, attaching chainplates before hull is cured and reccomended living with it.
At this stage I''m prepared to fair the hull and paint, with the understanding the hull may deflect in the future. I also plan to reinforce the interior hull with trapazoid styrofoam tabbed with glass.
If anyone reads this and thinks''''what the @^*@#!'''' this guy is nuts, please don''t hesitate to let me know
Thanks, spike
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Old 01-19-2006
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77 hunter hull dimple????

"Whiteboard" styrofoam is a really poor choice for a structural application, even if only used as a form for the final knee. Styrofoam is an opencell foam so water can move through and destroy any bond between the resin and the foam. Pink and Blue board, while not any better structurally is a closed cell foam and would make a better choice. (marine grade plywood would be an even better material.) You cannot use conventional polyester resin with these boards since the resins will melt the foam. You can only use Epoxy with stryrene based foams. I suggest that you shape the knees to fit and then lay them up with a minimum of a layer of roving and then a layer or two of cloth working with the parts off of the boat where layup will be much easier. Once cured, I would then suggest that you trim the new glass and then check your fit between the new piece to make sure that it is a good tight fit as trimmed. Then tab it to the deck and hull with a minumum of 3 layers of cloth extending out onto the hull and knee at least 6".

Jeff
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Old 04-27-2007
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Smile same hunter hull dimples

I have a Hunter 30 with the same dimples and come to the conclusion that this is not caused by manufacturing methods or structural problems. Its very unlikely this defect would every have been missed at the factory or dealer. I floated my boat with the mast off and saw no relaxation of the dimples. Hence, this is not a structural problem, but a permanent set in the materials caused by creep. I believe the problem is not serious over the lifetime of the boat. It occurs for three reasons: materials, stresses and time. The GRP hull material is a mixture of cross-linked polymer resins and glass fibers - both of witch will slowly stretch over time when a load is applied (or creep). An original thicker hull laminate would have prevented this. The stresses causing this are probably from the shrouds if the mast is left stepped on the hard, and the fore and aft support points of the craddle or jack stands are putting the sides of the hull in compressive shear stress (buckling load). Given enough time these forces will produce dimples. If there are no cracks or deck flexing, refair and paint. If this were "oil canning" under sail I would worry, but I have never seen this on my Hunter.
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Old 04-27-2007
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Originally Posted by sdudra2a
I have a Hunter 30 with the same dimples and come to the conclusion that this is not caused by manufacturing methods or structural problems. Its very unlikely this defect would every have been missed at the factory or dealer. I floated my boat with the mast off and saw no relaxation of the dimples. Hence, this is not a structural problem, but a permanent set in the materials caused by creep. I believe the problem is not serious over the lifetime of the boat. It occurs for three reasons: materials, stresses and time. The GRP hull material is a mixture of cross-linked polymer resins and glass fibers - both of witch will slowly stretch over time when a load is applied (or creep). An original thicker hull laminate would have prevented this. The stresses causing this are probably from the shrouds if the mast is left stepped on the hard, and the fore and aft support points of the craddle or jack stands are putting the sides of the hull in compressive shear stress (buckling load).
Doesn't this basically tell you that the boat was underengineered in that area. If it wasn't designed to have the dimple initially, and I seriously doubt that the hull form has a dimple in it.... the hull is too weak there to support the normal loads on it.
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Old 04-28-2007
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Define normal loads?
The boat was engineered and built thirty years ago. We have no Idea what PO's have done. such as over tensioning the shrouds leaving the mast stepped for years on end. What conditions this boat has seen or how it was treated. I will also make a leap here and say that more than likely you don't have the engineering spec's or the build spec's. Making an "under engineered" statement with just a tiny bit of anecdotal information is a bit of a stretch.
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Old 04-28-2007
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Brezzin-

Considering that the dimples are on most of the Hunters of that size and age... I would say it isn't a question of abuse, but of being under-engineered. Generally, if the dimple were an exception, and not the rule, I wouldn't think that it was under-engineered...but just a fact of that particular example. However, I've looked at Hunters in this size range and over a wide range of years, and many had similar characteristic dimpling.
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Old 04-28-2007
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Such dimpling over time is not unusual in Hunters OR in many other lightly laid up coastal production boats including a couple I have owned. I don't think it is a defect that will cause any problems assuming there is nothing else wrong at the chain plates and you aren't going blue-water.
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