Ixneigh wrote: ↑Tue Nov 10, 2020 8:00 pm
The bottoms of these boats are already fairly thick, in part because thick fiberglass was cheaper than installing more internal ballast. The keel will not fall off. It may get ground down or gnawed off by rocks I suppose. The keel is long enough and wide enough to support the full weight of the boat. In the common areas I let the boat dry out it’s grassy mud. On hard sand the boat may lean over a little. I’m pretty picky where I let the boat dry because of rocks, or in the Bahamas, conch. (!)
The keel should not be any deeper than the deepest part of the hull at any rate.
Ix
I am still re-getting the lay of the land on this forum. I am just getting to the point where I recognize someone's post and know enough about their other writings to judge how I "really" need to interpret their words. There are certain people already, that I know their writings will always be well thought out and something I should heed. JimmyT, Highlander, BOAT... others. I look to these people as experts in one thing or another. We all have varied backgrounds. Being an expert in one field does not necessarily carry over into others. A college degree doesn't give any overall superiority status. At my age, I've learned never to assume I "know it all". It only builds glass houses. I know day laborers that have taught me a thing or two. I sincerely appreciate this forum and its experts for what they are teaching me.
Not having crossed paths with your writings, I took your original post at face value only. At the very least, I should have noted your Admiral status. After Highlander's subtle rebuke, I did note that and since then... some of your other writings. I am sure your design is well thought out and will work.
However... for others that might launch their own design from this thread...
As I feel a need to give back to this forum and if I have
any expertise to offer, its analytical design and analysis of composite structures. The caveat to that... my background is with more exotic materials. I have never designed professionally with fiberglass matt and cloth (rovings) using polyester. IOW, I'd take someone's advice that has direct experience with fiberglass and actual knowledge of the Mac hull design.
I respectively disagree with Highlander's assessment that the Mac's hull is "hull for stout" and you can just do anything, anywhere. MacGregor's design has been optimized... whether it be from analytical design and analysis OR just good old iterative experience... MEANING... he didn't waste material where it was not needed. Yes, the hull will take 11000 lbs (sic) on the trailer... but move that trailer bunk back two feet and I am certain you will get a very bad experience.
Point being... I was in my boat all yesterday scrubbing the bilge. While the reinforcement where the trailer bunk IS hull for stout... probably somewhere between 1/2" and 3/4" thick, the hull underneath the aft bunk is closer to 1/4". It flexes quite easily under my weight. As your design stops at the bunk, I'd
guess you're good to go. But... I would not recommend anyone going back to the transom. If they used the same layup schedule mounting a keel in that area as they did forward of the bunk, it would overly stress that weak 1/4" floor. Just saying... bad things will happen.
On a lighter note...
I definitely have added you to my list of tutors. Your experience is far different than mine... and now that I'm retired, I may get to sail in grounds like you have every day. I've never thought about the shallow waters in the Keys nor having too much wind. Maybe, I need to consider that.