Listed Displacement vs. Max Displacement

[odlide]

I know there is a lot of old discussion on this, but I'd like to try again and keep it simple.

Is the Listed Displacement the "Maximum" Displacement (i.e., the weight of the water displaced when the waterline is at the painted boot stripe on the hull) or is it the "Delivered" Displacement (i.e., the weight of the water displaced the first time the boat is put in the water after taking delivery and before loading it with accouterments)?

So is the Listed Displacement the "Maximum" or the "Delivered" by the definitions above?

Thank you!

 

[PaulK]

It's not simple. Everyone has different definitions -- hence all the different terms you cite. Sometimes it's one thing, other times something else. It can be a number the Naval Architect calculated based on gear that he includes when he adds it up. You have to ask him what he includes. The stove or engine may be heavier or lighter than he thought, so it could be off. Sometimes the waterline is in the wrong place, too.

 

[JBP-PA]

Here is what Sail Boat Data has to say
"DISPLACEMENT: If you weigh the boat on a scale, that is her actual displacement. It is the weight of sea water that she will displace when she is afloat. Many designers figure displacement when half loaded with stores, liquids and crew. Some report light displacement which is the weight of the hull and permanent equipment but with empty tanks. Light displacement does not include stores, removable equipment (ex. Sails) or crew."

 

[dlochner]

The listed displacement is the designed displacement or the naval architects best guess as to the boats displacement. As @PaulK notes there are many places where weight can be added or subtracted. Use a little more resin in the build and the weight goes up, heavier sailcloth and the weight goes up. Install a lighter engine and weight goes down. And so forth.

The location of the waterline also depends on the actual weight of the boat and the water it is floating in. Boats in fresh water often sit lower in the water than in salt because fresh water is less dense.

SailboatData.com has a new interesting data point, pounds per inch of submersion, the amount of weight required to submerge the waterline by one inch.

 

[Crazy Dave Condon]

Is there a specific boat in the mix?

 

[odlide]

Is there a specific boat in the mix?

Looking for a trailer for my Cal 29.

Regarding the responses above, if some manufacturers use "Delivered" weight and others use "Maximum" weight as the Listed Displacement, how could you ever know which boat is heavier? You'd be comparing apples and oranges. Seems like there must be a standard (or something close to a standard).

A follow up question: Assuming the Listed Displacement is the "Delivered" weight of the boat, how do you find the "Max Load" (i.e., Maximum Displacement minus Delivered Displacement)? Or am I wrong to think that 30'-ish sailboats have a Maximum Displacement (and therefore lack a Maximum Load)?

Thanks again!

 

[dlochner]

Looking for a trailer for my Cal 29.

Regarding the responses above, if some manufacturers use "Delivered" weight and others use "Maximum" weight as the Listed Displacement, how could you ever know which boat is heavier? You'd be comparing apples and oranges. Seems like there must be a standard (or something close to a standard).

A follow up question: Assuming the Listed Displacement is the "Delivered" weight of the boat, how do you find the "Max Load" (i.e., Maximum Displacement minus Delivered Displacement)? Or am I wrong to think that 30'-ish sailboats have a Maximum Displacement (and therefore lack a Maximum Load)?

Thanks again!

Put the boat on the trailer, go to a truck stop and get the boat and trailer weighed. Launch the boat and then weigh the empty trailer. That will tell you precisely the weight of the boat. Trying to use builder's information will just drive you nuts. Use the builder's specs as a starting point and realize it is probably a low estimate of the boat's weight.

 

[odlide]

Trying to use builder's information will just drive you nuts. Use the builder's specs as a starting point and realize it is probably a low estimate of the boat's weight.

Good enough! Thank you!

 

[Crazy Dave Condon]

You should see a mfg tag on the trailer if used or new. You will see or find the weight of the trailer and then total weight to include trailer.
Once you know the weight of the boat, you will need to see if it falls within the allowed limits of weight being towed on the trailer. It sounds you are trying to find the specific weight of the cal 29.

Start with Sailboat Data and then the builder’s specs. Each builder must include dry weight to include boat, keel/rudder, mast/sails, diesel engine, head, galley, etc…
For your boat, I would suggest adding 500 pounds to get the weight of your boat. Then add another 10-20 per cent total weight of boat to the mix and see if that falls within the allowable weight to be towed for safety. You will need to confirm the tire load range too

I use to be a sailboat dealer and helped designing boat trailers

 

[Project_Mayhem]

"DISPLACEMENT: If you weigh the boat on a scale, that is her actual displacement. It is the weight of sea water that she will displace when she is afloat

This definition makes it sound like water and a boat weight the same per cubic foot

 

[Davidasailor26]

This definition makes it sound like water and a boat weight the same per cubic foot

No, rather the boat, on average, weighs less per cubic foot, thus its ability to float. Any object floating is displacing an amount of water whose weight exactly matches the total weight of the floating object. It

 

[Crazy Dave Condon]

The trailer you are looking for I would suggest four supports each side regardless of pads or bunk boards with a stout keel tray. If you intend to trailer launch, a long extension should be considered. One other thing, the axles need to be adjusted to distribute the load with a 10% of the load on the hitch to prevent the trailer from swaying. Brakes are required. Electric brakes are fine if hauling a boat with a travel lift;,otherwise, I recommend surge brakes. If you hav any questions , just ask. There are no stupid questions in this case

 

[odlide]

The trailer you are looking for I would suggest four supports each side regardless of pads or bunk boards with a stout keel tray. If you intend to trailer launch, a long extension should be considered. One other thing, the axles need to be adjusted to distribute the load with a 10% of the load on the hitch to prevent the trailer from swaying. Brakes are required. Electric brakes are fine if hauling a boat with a travel lift;,otherwise, I recommend surge brakes. If you hav any questions , just ask. There are no stupid questions in this case

Awesome, that all sounds very reasonable. And now to explore blister repair and bottom paint! But that's the subject of a different thread...

Thanks for all of the helpful input!

 

[Crazy Dave Condon]

@odlide
Take some pictures of the hull and post them here on blisters in a different thread If fouled with algae and/or barnacles, I would suggest a power washing of the hull first.