# Thread: Boat weights

1. Junior Member
Join Date
Aug 2017
Location
Lopez Island, WA, USA
Posts
3

## Boat weights

I am restoring a 1954 plywood Calkins Craft length 15 feet and need the weight to determine which trailer to purchase. Any takers?

2. Senior Member
Join Date
Apr 2015
Location
St. Helens, Oregon
Posts
994

## Re: Boat weights

Is this one of George's early skiffs or an early Bartender double ender? A pic would help, but I'd be betting you're looking at a hull weight around 800 lbs plus your motor.

3. ## Re: Boat weights

Trailors have a weight range, not an exact place. So lift the boat and guess. If two guys can pick it up, she weighs less than 200#. If it takes four, then maybe 400#. You'll end up close enough.

For more precision, get a couple of bathroom scales and put one under the bow and the other under the stern. Add.

Or lastly weight the darling. Make a two sling harness and attach a suitable (3:1 or 4:1 or whatever) tackle to something strong above and to the boat. Pull up a little so you've got the strain. Hang a livestock scale such as below on the line and pull the other end. Read the scale and multiply by the power of your tackle.

4. Junior Member
Join Date
Aug 2017
Location
Lopez Island, WA, USA
Posts
3

## Re: Boat weights

IMG_0850-1.jpgIMG_0851.jpgThanks for responding. With the pictures, does your estimate change?

5. ## Re: Boat weights

Decking and all. Could be 1,000#. Could be 500#. Measure the weight by approximation of scale. Too many variables for a guess from a photo.

6. Senior Member
Join Date
Dec 2011
Location
North East England
Posts
1,254

## Re: Boat weights

Originally Posted by Ian McColgin
Trailors have a weight range, not an exact place. So lift the boat and guess. If two guys can pick it up, she weighs less than 200#. If it takes four, then maybe 400#. You'll end up close enough.

For more precision, get a couple of bathroom scales and put one under the bow and the other under the stern. Add.

Or lastly weight the darling. Make a two sling harness and attach a suitable (3:1 or 4:1 or whatever) tackle to something strong above and to the boat. Pull up a little so you've got the strain. Hang a livestock scale such as below on the line and pull the other end. Read the scale and multiply by the power of your tackle.

You can use one scale, block at stern, scale at bow note weight. Then scale at stern and block at stern. Add the two weights

7. ## Re: Boat weights

That works. Most scales around here, very common on the fish pier, only go to 100#, which is why I added the winkle of using a tackel.

8. ## Re: Boat weights

Originally Posted by tink
You can use one scale, block at stern, scale at bow note weight. Then scale at stern and block at stern. Add the two weights
Make sure that the blocks and scales are put under exactly the same point on the hull ford and aft when you swap them around.

Originally Posted by Ian McColgin
That works. Most scales around here, very common on the fish pier, only go to 100#, which is why I added the winkle of using a tackel.
Allow for friction, multiply the weight by 1.05 for every sheave in the tackle.

9. ## Re: Boat weights

This is the method I use to keep track of weight during a build and also on a trailer. While I'm sure I did not invent it, I did derive it from simple static formulae. Probably too complicated for a multi axle trailer but very simple for a single axle one.

Weighing Your Boat at Home

This is a method which can be used to weigh a boat without having to transport it to a commercial scale. A small bathroom scale is used. The method is simple, accurate and may cause bystanders to marvel at your engineering whiz. It is particularly useful for weighing the boat during construction.

Weighing Off The Trailer

The boat is raised and supported by blocks placed near the longitudinal balance point on both sides under the chines or the sheer if it’s upside down. For the best accuracy, the support touching the hull should be crowned so that the actual point of support can be determined. The support points must be in a line perpendicular to the centerline and chosen such that there is a small amount of weight on the scale. A small board clamped to the transom can be used to contact the scale. Measure and record this weight, (W1) and the longitudinal distance from the measurement point and the supports, (D1). Now shift the balance points forward so that the weight on the scale is near the maximum that the scale can measure. Record this weight, (W2), and the distance moved, (D2). The weight of the boat is then:

Wb = (D1(W2 – W1)/D2) + W2

Weighing On The Trailer

If the boat is on a single axle trailer, the support point will be the axle and the scale will be under the tongue. The boat will then be moved on the trailer to get the differential weight, (W2 – W1) and distance, (D2). The weight of the boat is then:

Wb = D1(W2 – W1)/ D2

A trailer extension can be used to bring the weight, (W2), within the range of the scale if the boat is very heavy.

These formulas are derived by taking the sum of moments about the boat for both weight measurements. Since the sum of moments about a stationary object must equal zero, the two equations are set equal to each other and solved for boat weight, (Wb). Things that you don’t know, like the weight of the trailer and the center of gravity of the boat, cancel out.

The scale should be capable of measuring about 10 per cent of the boat weight for best accuracy and the distance moved, (D2), must be taken carefully. Measure the distance moved by marking a point near the trailer axle since measuring distance away from the bow fitting could be affected by flexing of the trailer tongue.

For boats light enough to be shifted on the trailer, the method is very easy. For heavier boats, move the boat during a partial launch at a ramp.

10. Senior Member
Join Date
Apr 2015
Location
St. Helens, Oregon
Posts
994

## Re: Boat weights

Very nice boat! Good score. Calkins tended to build robust boats, so I'm sticking to my 800# guess. What size motor are you putting on it?

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•