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Downeaster boat project

Old 10-09-2020, 11:44 AM
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Originally Posted by KP06 View Post
Not to go too far on a tangent, but doing my refit I calculated buoyancy based on measurements of 1’ sections and found the center of buoyancy at the desired/design watering. Then using water drums during a float test as well as running across a truck scale determined my center of gravity and rough layout. Rather than all this backyard arithmetic how would you lift the lines of an existing hull to run the calculations and determine the weights of the existing layup?



Calculated displacement in 1’ sections at desired water line and converted through cubic inches of displacement to cubic feet to pounds salt water displaced to determine Center of buoyancy was roughly 8’ forward of the transom.
KP60 I'm trying to figure out what the numbers in your columns represent, would you mind to explain that I little more. It looks like the first column is the station in feet but thats about all I can figure out.
Old 10-09-2020, 01:46 PM
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Originally Posted by surv View Post
KP60 I'm trying to figure out what the numbers in your columns represent, would you mind to explain that I little more. It looks like the first column is the station in feet but thats about all I can figure out.
First column is the station # in feet starting at the transom.

Second column is the cubic inches displaced at that station.

Third is converted to cubic feet.

I’ve misplaced the next “sheet” but then I converted to pounds of Salt water displaced (63lbs/cubic foot)

On the right side of the attached is the total displacement at the desired full load waterline in pounds.

So when I launched and simulated with water drums she rode so high out of the water I knew my bulkheads and deck needed to be beefy to get her down in the water a bit more. Also added another couple layers of cloth to the bottom shell. All that weight down low should make her ride nicely and with the fuel tank pushed forward and batteries in the console should be good to go. Going to get the engines rigged and run the bot before final fairing and paint.

Ive never seen my hull underway and want to make sure she’s balanced right and no major mods are needed before finalizing the bright work.

Nothing could be worse than spending weeks fairing and painting then have to cut back open for something...
Old 10-20-2020, 07:38 PM
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I've been working on the transom bracket, the main box is about finished up. Still need to build the platform and probably add a small support down the center.

Here are a few pictures.















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Old 10-24-2020, 06:41 AM
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Your curved mold process is excellent study material. Thank you for that level of detail.
Old 10-25-2020, 01:53 PM
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Originally Posted by KP06 View Post
Your curved mold process is excellent study material. Thank you for that level of detail.

Thank you KP06, I hope that it helps you or anyone else with something they are working on.

I enjoy watching your project as it comes together. Your doing a great job on it, keep up the good work.
Old 10-25-2020, 05:45 PM
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I started putting some numbers together to try and figure out where the center of gravity is. Some of my calculations are rough math and a fair amount of guess work but I think the CG lands about 4.5-5' forward of the transom. This is including the engine on the bracket with 24" setback. I dont know if thats god/bad or otherwise. If anyone wants to comment on what they think I would appreciate the feedback.
Thanks.
Old 10-29-2020, 11:11 AM
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Depending on the boat you want to be between 25% and 30% of the waterline length of the hull (not bracket) as rule of thumb. There are exceptions and lots of things that play into it, like the speed, bottom geometry, how the weight is distributed, plus much more and it is all interconnected. But, for those running hulls that have been around for years, you don't have to do much more than look around to see where the ideal placement of weight is to get close. But when designing a new hull making assumptions are quite risky. I know of more than one instance where the first boat of a mold was a disaster because of weight placement. One in particular has a retail price of several hundred thousand dollars with a long wait list. When asked he said "I didn't wanna pay for it" (the weight study), so off to cutting they went to move weight around and try again...……….
Old 10-29-2020, 02:35 PM
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Originally Posted by ADAM87 View Post
Depending on the boat you want to be between 25% and 30% of the waterline length of the hull (not bracket) as rule of thumb. There are exceptions and lots of things that play into it, like the speed, bottom geometry, how the weight is distributed, plus much more and it is all interconnected. But, for those running hulls that have been around for years, you don't have to do much more than look around to see where the ideal placement of weight is to get close. But when designing a new hull making assumptions are quite risky. I know of more than one instance where the first boat of a mold was a disaster because of weight placement. One in particular has a retail price of several hundred thousand dollars with a long wait list. When asked he said "I didn't wanna pay for it" (the weight study), so off to cutting they went to move weight around and try again...……….

Thank you for the reply ADAM87! I appreciate you sharing some knowledge on the subject.

I think I'm close to the 25-30% mark so maybe this thing will work. I'm going to continue with the transom bracket build and if after a sea trial I cant get it to work I'll get out the saw and make this boat a standard transom mount.
Old 11-01-2020, 06:54 PM
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Can’t believe I haven’t read this thread yet. I appreciate the insight and Encouragement on my thread, just read the whole thing and have to say you have done some serious work here. I honestly may have done a stringer grid similar to yours had I seen it. Love all the mold work. Great job man keep pushin!!
Old 11-01-2020, 07:50 PM
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Originally Posted by SEABIRD254 View Post
Can’t believe I haven’t read this thread yet. I appreciate the insight and Encouragement on my thread, just read the whole thing and have to say you have done some serious work here. I honestly may have done a stringer grid similar to yours had I seen it. Love all the mold work. Great job man keep pushin!!

Thanks Seabird!
Old 11-04-2020, 04:59 PM
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Ive been working on the swim platform for the transom bracket, here are some progress pictures I wanted to share.




This is the bottom side with some temporary forms made to form the lip around the perimeter.




Another picture of the temporary forms with some blue painters tape on them. I didnt use any wax because I dont want to deal with removing it but painters tape makes a good barrier between the wood and the fiberglass without to much effort removing it.




The temp. forms are removed and sides cleaned with acetone then a light skuff with the grinder.




This is the top side with one layer of csm on it. I'll be working on the radius around the corners so I can wrap the fiberglass down the sides when I laminate the top.
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Old 11-04-2020, 05:05 PM
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Really cool, slow and steady gets it done. Looking great
Old 11-04-2020, 05:37 PM
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Looking great. Try packing tape next time for a barrier the glass/resin won't stick to. Easier to remove and leaves a smoother finish.
Old 11-04-2020, 07:00 PM
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looks awesome. Ive had good luck with clear packing tape. Have you ever used the 1/8" melamine board? bends easy and doesnt stick, its like masonite with a melamine coating. bends easy would save time on those corners. i think theres a thin plastic sheeting at the big box stores which would work too.
Old 11-04-2020, 07:34 PM
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Originally Posted by nevets View Post
Really cool, slow and steady gets it done. Looking great

Thank you Nevets! I agree.
Old 11-04-2020, 07:40 PM
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Originally Posted by DOYAM View Post
Looking great. Try packing tape next time for a barrier the glass/resin won't stick to. Easier to remove and leaves a smoother finish.
Originally Posted by SEABIRD254 View Post
looks awesome. Ive had good luck with clear packing tape. Have you ever used the 1/8" melamine board? bends easy and doesnt stick, its like masonite with a melamine coating. bends easy would save time on those corners. i think theres a thin plastic sheeting at the big box stores which would work too.
Thank you!

I'll have to try packing tape some time. I haven't tried using thin melamine board but I bet it would work great.
Old 11-05-2020, 02:53 AM
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Looks great Surv, no surprise! Flash tape is what we use at work. It’s pricey at $25 a roll from Amazon but it’s designed for this.
Old 11-05-2020, 05:28 AM
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Originally Posted by 2TDave View Post
Looks great Surv, no surprise! Flash tape is what we use at work. It’s pricey at $25 a roll from Amazon but it’s designed for this.

Thanks Dave! I'll look up flash tape, not sure I have ever seen it.
Old 11-05-2020, 06:29 AM
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You make it look easy!
Old 11-19-2020, 06:03 PM
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I got the transom bracket finished and installed it. I debated on installing it with bolts and 5200 but ended up using thickened resin to bond it then tabbed it all the way around the perimeter. It will also get bolted to the transom but the bolts are there more less as a safety.

Here are some pictures.













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