Dinghy attachment to boat deck

I too like the silicone in the screw heads, a very nice touch.

I have run a boat with removable chaulks like that. I would highly recommend making a wooden dowel that goes between the two of them (bolts) through the eye hole to keep them from rotating loose in a rough sea and coming out. I have had that happen before with that same design, from the same place.

First off- resize the photo's so they fit in the screen. Many liferafts and dingys are attached with screws not thru bolted. I had the liferaft on the bow for many many years with screws and no issues. UMT is a AFAIK a reputable company- do you think they are cutting corners with the screws? Ask around and I think you'll find it's standard/acceptable to do what they are doing and you should have no problems if installed properly. BTW- I've had tef-gel on outside dis-similar metals with zero corrosion/galling after 6 years, and I'm not the only one who knows about this "magic snake oil". You make the call on the gel- listen to someone who doesn't use it and then dismisses it as snake oil, or someone who does and the results are proven.

Hi,

Tef Gel works ok and so does natures very own Lanolin, the latter is even a reasonable anti fouling according to a couple of Trawler operators I once talked to.

As for having your liferaft on the foredeck, I guess that is an easy way to get into it when it is washed onto the sundeck.

You must be very lucky with your weather to be able to carry those sort of things on the foredeck.

The fitting looks fine, but over the years I have witnessed many fittings that were screwed down being ripped out. I highly recommend that it is through bolted with a large backing plate and some thought as to how to deal with core material compression. Several options there, delron blocks, dig out as much core material as possible and flood with epoxy resin the list goes on.

"But, this advice contradicts information I've read in Steve D'Antonio's and David Pascoe's articles ..."

Pascoe? Oh, yeah the guy who tells his clients that the fuel in a diesel is compressed in the cylinder until it is hot enough to explode.

After looking at the photos of the screw mounts you posted, I thought virtually all of the advice posted was in agreement with both Steve D'Antonio and Dave Pascal's publishings? In a nutshell, f the deck is cored and you are trying to support a heavy weight on localized points, you need to consider the crushing issue. Whether it be a metal or composite fill-in, tapped or not, something needs to transfer the loads between skins, period.

The two big factors in any composite laminate are the skin composition and core thickness. Both directly affect the decks properties and can allow you to "get by" with less than optimum mountings. If, for example, you have a deck that has about 1/4" thick glass on both sides and a core of 3/4" (typical for polyester based decks), your dinghy would probably sit just fine on those mounts without any backing, filling or anything but screws into the top skin and would likely stay there unless you were in some really bad conditions.

If it was a "higher tech" deck built to optomize the structure such as an epoxy based, vacuum-bagged laminate, the skins would likely be much thinner and the core thicker. Those thinner skins wouldn't hole the screws and the deck would probably dimple in short order unless you had some type of insert.

Properly engineered, both methods will produce a strong deck, but the bagged, lighter weight deck will need extra attention because it's skins will likely be much thinner and can't spread the loads as easily as the thicker ones would of the heavier deck.

I didn't intend to get too technical but I wanted to show how it isn't quite so simple a solution to just mount something on a composite structure without knowing all the details of her construction beforehand. If I'm not mistaken, didn't you host a herd of talent from these very pages during the boat show? The expense of a cold beverege or two sure would have been cheap compared to a naval architects fee for a design analysis, even if it had to be ran through a universal translator in the morning to make sense of it

Well said!

hello dan1000,

I would never through-bolt a core without reinforcement ... you will finish uo flexing the skins and crushing the core.
Nor would I ever embed metallic sleeves.

Perhaps you might like to consider this approach

1 .. drill your bolt holes directly through both skins and core

2 .. bend the tip of a small nail (several mm larger than the bolt) to act as a router, attach it to a small battery drill, angle it into each bolt hole and clean out the core... then carefully vacuum out the core holes ... make certain you get all the loose material out of the holes

3 .. masking off the under skin holes with masking tape

4 .. mix your epoxy and very carefully work it into the holes from the top side avoiding any air pockets.

5 .. after the epoxy has set hard, sand off any expansion excess

6 .. redrill the core and through bolt the fitting using whatever 'sticky stuff' you favour for waterproofing

Have a beer (or two) because now you have joined the high-tec composite team

hope this helps

Yeah, and his mailbox probably needs cleaning out too!

Glad it all worked out for you.

hamall9 is the man! I have a similar project and I will try you method. Thanks
Tim

It is very important to preserve the core at all times and resist the urge to take a shortcut and screw a fitting thru it in an unprepared manner.

Even screwing a hose bracket into the inner skin is a big no no ... no matter how short the screw ... in this case you should epoxy a pad [plywood] to the inner skin and then screw into the pad without touching the skin.

goodluck
h9