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Boat Physics

M2MC@aol.com

Wed, Mar 2, 2005 2:50 PM

I just had my boat hauled out and we added a Atkins Hoyle standpipe power
davit to the stern of the boat to lift a 10' Livingston dinghy to the back
sundeck. My boat is a 44' Marine Trader sundeck model. The dinghy is 60" wide
and weighs approximately 150 lbs. I estimate the weight of the standpipe
davit with winch, boom, 12v battery (added below deck next to the standpipe) etc.
to be less than 250 lbs. So I've essentially added approximately 400 lbs.
to the back 6 feet of my 44 foot boat. My concern is my waterline. Prior to
adding the standpipe and dinghy I had approximately 7" of bottom paint
showing above the waterline in the back of the boat and about 2" showing at the bow
of the boat. (All of these weights and measurements are approximate because
I never expected a significant change adding approximately 400 lbs - a
lesson learned, if somewhat late). I now have about 3" of bottom paint showing
above the waterline at the stern and about the same 2" showing at the bow.
My through hull outlets are now about 4" above the water instead of 6 or 7"
above the water. No other weight was added or moved on the boat. Physics is
certainly not one of my strengths so I don't understand why 400 lbs. would
have lowered the back of the boat by 3 or 4 inches in the water? I also would
have expected the front of the boat, at the water, to have been raised an
inch or two if the back lowered by 3 or 4 inches. And finally how high above
the water should the thru hull outlets be for safety? Any input is
appreciated.
Mike Coble
"Twocan"

I just had my boat hauled out and we added a Atkins Hoyle standpipe power davit to the stern of the boat to lift a 10' Livingston dinghy to the back sundeck. My boat is a 44' Marine Trader sundeck model. The dinghy is 60" wide and weighs approximately 150 lbs. I estimate the weight of the standpipe davit with winch, boom, 12v battery (added below deck next to the standpipe) etc. to be less than 250 lbs. So I've essentially added approximately 400 lbs. to the back 6 feet of my 44 foot boat. My concern is my waterline. Prior to adding the standpipe and dinghy I had approximately 7" of bottom paint showing above the waterline in the back of the boat and about 2" showing at the bow of the boat. (All of these weights and measurements are approximate because I never expected a significant change adding approximately 400 lbs - a lesson learned, if somewhat late). I now have about 3" of bottom paint showing above the waterline at the stern and about the same 2" showing at the bow. My through hull outlets are now about 4" above the water instead of 6 or 7" above the water. No other weight was added or moved on the boat. Physics is certainly not one of my strengths so I don't understand why 400 lbs. would have lowered the back of the boat by 3 or 4 inches in the water? I also would have expected the front of the boat, at the water, to have been raised an inch or two if the back lowered by 3 or 4 inches. And finally how high above the water should the thru hull outlets be for safety? Any input is appreciated. Mike Coble "Twocan"

Oliver Brassard

Wed, Mar 2, 2005 11:00 PM

Mike,

I may be wrong, but recently I've been checking out hull designs & specs.
I Believe one of the specs or parameters to "measure" a particular hull
against other designs is the amount of weight required to change the
waterline by 1". I seem to remember that it is a pretty high number (like in
excess of 2000 lbs) to change the waterline by an inch on a typical semi-D
trawler hull.If that's true your loosing 3" of waterline height would equal
6000lbs? Maybe I'm wrong about this. Gettin' old you know.
Oliver

-----Original Message-----
From: trawlers-and-trawlering-bounces@lists.samurai.com
[mailto:trawlers-and-trawlering-bounces@lists.samurai.com]On Behalf Of
M2MC@aol.com
Sent: Wednesday, March 02, 2005 9:50 AM
To: trawlers-and-trawlering@lists.samurai.com
Subject: T&T: Boat Physics

I just had my boat hauled out and we added a Atkins Hoyle standpipe power
davit to the stern of the boat to lift a 10' Livingston dinghy to the back
sundeck. My boat is a 44' Marine Trader sundeck model. The dinghy is 60"
wide
and weighs approximately 150 lbs. I estimate the weight of the standpipe
davit with winch, boom, 12v battery (added below deck next to the
standpipe) etc.
to be less than 250 lbs. So I've essentially added approximately 400 lbs.
to the back 6 feet of my 44 foot boat. My concern is my waterline. Prior
to
adding the standpipe and dinghy I had approximately 7" of bottom paint
showing above the waterline in the back of the boat and about 2" showing at
the bow
of the boat. (All of these weights and measurements are approximate
because
I never expected a significant change adding approximately 400 lbs - a
lesson learned, if somewhat late). I now have about 3" of bottom paint
showing
above the waterline at the stern and about the same 2" showing at the bow.
My through hull outlets are now about 4" above the water instead of 6 or 7"
above the water. No other weight was added or moved on the boat. Physics
is
certainly not one of my strengths so I don't understand why 400 lbs. would
have lowered the back of the boat by 3 or 4 inches in the water? I also
would
have expected the front of the boat, at the water, to have been raised an
inch or two if the back lowered by 3 or 4 inches. And finally how high
above
the water should the thru hull outlets be for safety? Any input is
appreciated.
Mike Coble
"Twocan"

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Mike, I may be wrong, but recently I've been checking out hull designs & specs. I Believe one of the specs or parameters to "measure" a particular hull against other designs is the amount of weight required to change the waterline by 1". I seem to remember that it is a pretty high number (like in excess of 2000 lbs) to change the waterline by an inch on a typical semi-D trawler hull.If that's true your loosing 3" of waterline height would equal 6000lbs? Maybe I'm wrong about this. Gettin' old you know. Oliver -----Original Message----- From: trawlers-and-trawlering-bounces@lists.samurai.com [mailto:trawlers-and-trawlering-bounces@lists.samurai.com]On Behalf Of M2MC@aol.com Sent: Wednesday, March 02, 2005 9:50 AM To: trawlers-and-trawlering@lists.samurai.com Subject: T&T: Boat Physics I just had my boat hauled out and we added a Atkins Hoyle standpipe power davit to the stern of the boat to lift a 10' Livingston dinghy to the back sundeck. My boat is a 44' Marine Trader sundeck model. The dinghy is 60" wide and weighs approximately 150 lbs. I estimate the weight of the standpipe davit with winch, boom, 12v battery (added below deck next to the standpipe) etc. to be less than 250 lbs. So I've essentially added approximately 400 lbs. to the back 6 feet of my 44 foot boat. My concern is my waterline. Prior to adding the standpipe and dinghy I had approximately 7" of bottom paint showing above the waterline in the back of the boat and about 2" showing at the bow of the boat. (All of these weights and measurements are approximate because I never expected a significant change adding approximately 400 lbs - a lesson learned, if somewhat late). I now have about 3" of bottom paint showing above the waterline at the stern and about the same 2" showing at the bow. My through hull outlets are now about 4" above the water instead of 6 or 7" above the water. No other weight was added or moved on the boat. Physics is certainly not one of my strengths so I don't understand why 400 lbs. would have lowered the back of the boat by 3 or 4 inches in the water? I also would have expected the front of the boat, at the water, to have been raised an inch or two if the back lowered by 3 or 4 inches. And finally how high above the water should the thru hull outlets be for safety? Any input is appreciated. Mike Coble "Twocan" _______________________________________________ http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering To unsubscribe send email to trawlers-and-trawlering-request@lists.samurai.com with the word UNSUBSCRIBE and nothing else in the subject or body of the message. Trawlers & Trawlering and T&T are trademarks of Water World Productions. Unauthorized use is prohibited.