Boat Specs - Weight

[ptrailsail]

Hello,
I'm new to boats, looking to figure out lots of stuff, but I have one doubt that I must clarify upfront.
When I look at specs for a boat, usually there is the indicated displacement and then the ballast weigth.
What is the actual total weigth of the boat, for trailering?
Do I have to add the two or is the ballast just fyi?
Or is that no usefull indication of trailerable weigth and I must check some other way?

I have a fairly limited towing weigth for my car, 1180kg or 2600lbs, and that will have to include the trailer along with outboard engine, etc... so I need to figure this out first...

Thanks for any help.
Pedro.

[goat]

Displacement is the weight you're looking for. It's actually the weight of the water that would be displaced when your boat is floating, but for your case it's close enough to the weight. Ballast is weight placed below the waterline to help right the boat and is already added to the displacement.

Be sure to add the weight of all the stuff you put on the boat to the total weight; water, fuel, batteries, dinghy, food etc.

This is a simplified explanation, you could get into all kinds of discussions on the intricacies of densities etc, and if I know this forum it probably will.

goat

[Steadman Uhlich]

Originally Posted by goat

Displacement is the weight you're looking for. It's actually the weight of the water that would be displaced when your boat is floating, but for your case it's close enough to the weight. Ballast is weight placed below the waterline to help right the boat and is already added to the displacement.

Be sure to add the weight of all the stuff you put on the boat to the total weight; water, fuel, batteries, dinghy, food etc.

This is a simplified explanation, you could get into all kinds of discussions on the intricacies of densities etc, and if I know this forum it probably will.

goat

Good answer.

One small correction:

The ballast weight is INCLUDED in the determination or calculation of the displacement of the boat, not "added to" the weight of the boat.

For the OP: The ballast is considered a part of the boats designed total weight. It is listed separately so buyers can know how much of the total weight (displacement) is ballast. Two different boats of the same displacement could have very different amounts of ballast included to make them stabile when floating in the water.

[chris95040]

Originally Posted by goat

It's actually the weight of the water that would be displaced when your boat is floating, but for your case it's close enough to the weight.

Displacement is _exactly_ the weight of the boat, and _exactly_ how much weight in water it would displace when floating.

Original poster, displacement = total weight of the boat, *including* the ballast.

Ballast is typically a specific bit of weight placed low on the boat for stability.

So you can tow a boat who's displacement is 2600 pounds (minus the weight of the trailer).

[cabo_sailor]

Don't forget tongue weight. Your vehicles towing capacity is limited by both. This will also dictate what class hitch you need.


Sent from my iPhone using Cruisers Sailing Forum

[denverd0n]

Originally Posted by chris95040

Displacement is _exactly_ the weight of the boat, and _exactly_ how much weight in water it would displace when floating.

True, in actuality, for each boat. But a little misleading, I think, since we are talking about the published specifications here, and almost no boat ever weighs "exactly" the same as its designed displacement. There are always some differences, and sometimes they are significant.

What's more, the moment you add anything to the boat that the designer did not include in his calculations, then the boat weighs (and displaces) more than the published displacement specification. Which is why...

Originally Posted by chris95040

So you can tow a boat who's displacement is 2600 pounds (minus the weight of the trailer).

This is only true if the boat has no additional kit, whatsoever, in it. Otherwise, as goat said: "Be sure to add the weight of all the stuff you put on the boat to the total weight; water, fuel, batteries, dinghy, food etc."

[chris95040]

Originally Posted by denverd0n

True, in actuality, for each boat. But a little misleading, I think, since we are talking about the published specifications here, and almost no boat ever weighs "exactly" the same as its designed displacement. There are always some differences, and sometimes they are significant.

What's more, the moment you add anything to the boat that the designer did not include in his calculations, then the boat weighs (and displaces) more than the published displacement specification. Which is why...


This is only true if the boat has no additional kit, whatsoever, in it. Otherwise, as goat said: "Be sure to add the weight of all the stuff you put on the boat to the total weight; water, fuel, batteries, dinghy, food etc."

Really good, important points.

[Stumble]

Don't forget to count the weight of the trailer. A twin axle steel trailer for a 20' boat can easily top 1,100 lbs.

[newhaul]

A web site that you will find valuable for all the info for most sailboats like weights layouts sail areas and the like is. WWW.sailboatdata.com

[ptrailsail]

Well Thanks for all the great info everyone!

"A twin axle steel trailer for a 20' boat can easily top 1,100 lbs"

Well, I saw some trailers allready and the maximum I found was around 200kg or around 440lbs, maybe they were aluminium, but I'll be watching for that, thanks for the heads up.

As for the weigth of all the stuff that goes in the boat, maybe I'll start a new thread, not go off this topic.

Thanks again, you just helped me move forward in my quest

[Cadence]

I may be wrong. I was under the impression that displacement was the weight of the displaced water when loaded to the design waterline.

[sailjumanji]

Probably need to tell us what boat you are considering. My BIL has a water ballasted Hunter. The water is drainned out as it comes up the ramp. You would not need to consider that weight for towing.

[Terra Nova]

Originally Posted by chris95040

Displacement is _exactly_ the weight of the boat...

Not exactly.

Cadence is correct. Displacement includes even fuel and water (50% full?).

[Cadence]

Originally Posted by ptrailsail

Hello,
I'm new to boats, looking to figure out lots of stuff, but I have one doubt that I must clarify upfront.
When I look at specs for a boat, usually there is the indicated displacement and then the ballast weigth.
What is the actual total weigth of the boat, for trailering?
Do I have to add the two or is the ballast just fyi?
Or is that no usefull indication of trailerable weigth and I must check some other way?

I have a fairly limited towing weigth for my car, 1180kg or 2600lbs, and that will have to include the trailer along with outboard engine, etc... so I need to figure this out first...

Thanks for any help.
Pedro.

I wouldn't worry about it. Us common sense. And frankly, it is what you can pull up a ramp on it's grade. I don't think there is a magic number.

Best of luck.

[sailjumanji]

I hate to tell you this, but relying on published weights is problematic. I have done ratings for multihulls - including many trailerable boats - for years. What we find for even manufacturer's that actually weigh their boats is that a particular model can vary 10% to sometimes 15%. Maybe it is uncalibrated load cells, or maybe even manufacturing variation. Plus there is no standard - do you include the mast, boom, sails, battery, motor? Weight is such a huge performance variable for the Corsair trimaran fleet, that we had specific rules for weighing the F-31's- what had to be on the boat, etc. Easiest way was usually to weight the boat and trailer, launch the boat, and weigh the trailer. Even then there would be a 200 lb difference on the same boat from one year to another, which was due to scale calibration. And these boats were in the 3,000 lb category. Other manufacturers were much larger variation. So if you are trying to guess at 10 lbs, 50 lbs, or a couple of hundred pounds only to play with before overloading your rig, I think it's not reliable.

PS. The trailerable tri's are a piece of cake compared to trying to understand what a Lagoon weighs, or a one-off build. We have a 39 ft cat that weighs less than 7000 lbs (TRT 1200) and some condo-cats the same length probably around 25000 lbs.