What does your boat weigh?

Designs for inboard or outboard power

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Hercdrvr
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What does your boat weigh?

Postby Hercdrvr » Sun Apr 02, 2017 12:31 pm

I'm trying to guesstimate the weight of my Malahini to buy the right pitch prop on the 1st try. Plans say hull is 475 lbs, I used lots of white Oak and an Ash floor, etc. Rough guess is 600lbs plus motor and fuel so maybe about a 1000lbs.
Anyone with real numbers, not just guesses?

Matt B

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Bill Edmundson
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Re: What does your boat weigh?

Postby Bill Edmundson » Sun Apr 02, 2017 1:50 pm

Matt

Hull weight is generally what it will weigh at the flip(about half of the raw boat weight..) We'll need to add fuel, people, and gear, and a guess at the motor weight. With the HP and WOT RPM I can give you a guess at the prop.

Bill
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JimmY
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Re: What does your boat weigh?

Postby JimmY » Sun Apr 02, 2017 2:39 pm

Take it to a junk yard, they usually have scales for weighing scrap metal in vehicles. in Michigan, you have to weigh your trailer to get a license, and that's where I took my last sailboat trailer.
-Jim
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gdcarpenter
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Re: What does your boat weigh?

Postby gdcarpenter » Sun Apr 02, 2017 3:03 pm

My ZIP, slightly smaller than the Malahini, fully loaded for a days outing, weighs in a little under 800 pounds. I suspect my ZIP is lighter than most ZIPs.
That's with White Oak framing, big battery, 6 gallons of fuel plus an extra emergency one gallon back up, anchor, and all safety equipment. My engine is lighter than most as the 1959 Mark35A is rated at about 135 lb.
At 35 HP my outboard pushes my ZIP to 30 MPH @ 5,600 RPM with a 3 blade, 10" diameter, 10" pitch prop.
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

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mrintense
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Re: What does your boat weigh?

Postby mrintense » Sun Apr 02, 2017 3:20 pm

I too am interested in the weight of my boat. The only things I have to go on are the displacement figures in the plans and one builder in England who told me his boat weighed 3500 pounds with the trailer (fully loaded).
Carl
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Hercdrvr
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Re: What does your boat weigh?

Postby Hercdrvr » Sun Apr 02, 2017 8:32 pm

Bill ,
So your saying if the plans say hull is 475lbs the finished boat is about 950 plus everything else....motor, fuel, etc?
Hull--------950
Motor------260
Fuel--------100
Battery-----50
Other-------100

= 1460lbs

Does this sound reasonable for a Malahini?

Found this on trailer weights

https://www.glen-l.com/designs/trailer/trailer-wts.html

gdcarpenter
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Re: What does your boat weigh?

Postby gdcarpenter » Mon Apr 03, 2017 3:49 am

Given my ZIP weighs 800 lb., minus 375 lb. (completed hull weight estimated by GlenL), that means the 'build out' after hull completion, with engine, electrical, and accessories, added 425 lb. My deck boards are only1/8" thick (a third thinner/lighter than most) and my sole boards are 5/16" thick (about a third thinner/lighter than most), and I have minimal front seat weight.

Given the Malahini estimated hull weight of 475 lb. (100 lb. more than a ZIP), add an extra 150 lb.for your heavier motor, and an extra 50 lb. for a larger fuel tank, that would 'ballpark guesstimate' your finished weight around 1,00 lb. minimum, more closer to 1,200 lb.

I used transport truck weight scales to weight truck with boat and engine, and trailer - then reweighed with truck alone, then removed boat from trailer and subtracted weight of trailer to get my actual boat weight.
This is my first, last and only boat build.

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Bill Edmundson
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Re: What does your boat weigh?

Postby Bill Edmundson » Mon Apr 03, 2017 7:23 am

Matt

The boat weight at 950# seems a little high. If we say 800#. 100# of gasoline is about 15 gal.@ 6.2 #/gal. Is that right? That will get you to about a 1300# trailering weight.

For sizing the prop we need to add people. I think, USCG says 150#/person=600#. I would just add your weight and try to get the max of WOT rpm range.

Bill
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Hercdrvr
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Re: What does your boat weigh?

Postby Hercdrvr » Mon Apr 03, 2017 8:01 am

All that said...13.25 x 17 aluminum prop, 3 blade prop sound like a good prop? It's a 90hp as most of y'all know.

Matt B

PeterG
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Re: What does your boat weigh?

Postby PeterG » Mon Apr 03, 2017 8:20 am

I calculated the displacement and therefore the total weight of the Malahini based on the design waterline shown on the plans and using the Simpson's Rule method described on page 20 of the Glen-L Boatbuilding 101 booklet. I came up with about 1350 lbs at the design waterline. That figure represents the combined weights of the hull, motor, gear, fuel, people, etc. I used it to find the matching prop for my 1965 Mercury 650 outboard, which my Mercury Shop Manual says should be a 12" dia. x 17" pitch 3-blade or a modern equivalent to get the 4800 to 5300 max RPM.
Sounds like you're very close with that prop.
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Bill Edmundson
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Re: What does your boat weigh?

Postby Bill Edmundson » Mon Apr 03, 2017 8:34 am

Matt

I would run it first and see where you WOT rpm is. Do you know the gear ratio?

Edit: With 90hp, 1500#, gear ratio of 2.33:1 and, 10% slip, I come up with a pitch of 21". Max. 5500 rpm.

Try what you have first!

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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Hercdrvr
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Re: What does your boat weigh?

Postby Hercdrvr » Mon Apr 03, 2017 8:48 pm

Yamaha 90 is a 2.00 to 1 gear ratio.

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Bill Edmundson
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Re: What does your boat weigh?

Postby Bill Edmundson » Mon Apr 03, 2017 9:12 pm

That should get the pitch close to what you have. With a 2:1 gear, I came up with a 18" pitch @ 2750 rpm shaft speed.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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