Draft: Bare or Loaded?

[Jonah]

Hi all,

No response from Grady on this, so thought I'd post it here.

The brochure for my (new to me) 1995 Sailfish 272 lists the draft as 18". Is this the draft when the boat is 'bare' (no fuel, no equipment, no outboards), or fully loaded? If the former, then does anyone have an easy way to estimate the increase in draft with 200 gallons of fuel and two Yamaha 225HP outboards?

Thanks as always.

 

[DennisG01]

How long ago did you contact GW? They're usually pretty good at getting back to people.

Anything stated in boat (and manufacturer) manuals, if not specifically specified, will always be bare. I do not know of any way to "estimate" the increase in draft with a loaded boat. Most likely, your boat sits a little deeper than 18" to start with since it's 23 years old is probably a little heavier due to moisture absorption. Overall, though, I don't think from bare to loaded will be more than 6" - I think that would be a safe guess, anyways. Measure it and see!

 

[seasick]

This is not scientific at all but you can make an estimate which will get you an approximate scale of change.
If the hull was square and flat and the additional load was evenly distributed, then estimates would be pretty close.
Since loads are not generally evenly distributed and hulls are not square and flat. The estimates is a lot more complex but let's give it a try. Lets say the bare hull weighs 5000 pounds. If the hull were flat and uniform in shape ( square, rectangular, round, it doesn't matter) then an 18 inch draft would equate to 278 pounds per inch of displacement.
Add 1000 pounds of gear and the hull will sit a little over 3 1/2 inches lower.
In the real world, hulls are not flat and V hulls actually present more hull to the water as they sit lower. That will reduce the inches per extra weight. At the same time the stern is a bigger area to the water so weigh added up front can have a larger effect than weight added in the rear

 

[Finest Kind]

Just keep an eye on the color of the water ahead, remember this, and you wont have to worry about your draft:

Brown, brown, run aground!"

 

[glacierbaze]

When in the water, make a mark, or a mental note, where the water line is. On the trailer, measure from that mark to the ground, and subtract from the ground up to the bottom of lower unit. That is your actual draft at float. On plane or plowing will differ.

 

[seasick]

Just keep an eye on the color of the water ahead, remember this, and you wont have to worry about your draft:

Brown, brown, run aground!"

That works in Bermuda but not so much in Jamaica Bay NY. At times all the water is brown and it is rarely blue

 

[Jonah]

Thanks Everyone,

Dennis: I submitted the request about a week ago. I agree, they are usually very quick. I'll post here again if I get a helpful reply.

Seasick: I'll do some tweaking to your suggestion (actual weight was originally 5,500lbs, potentially a bit more as Dennis mentioned), and see what I come up with. I bet I have the outboards' weight in the manuals, too.

Glacierbaze: I like it, but unfortunately I have no trailer here.

Thanks again everyone.

 

[DennisG01]

It's true that all hulls absorb moisture over time. But, in "normal" cases, the amount of weight it's going to add VS how much deeper a boat sits is not going to be a whole lot. But, I was/am unsure how accurate of an answer you were looking for - which is why I offered that.

I'm curious - why the need to know such a specific number? Can you not just add the weight (even "fake" weight such as sand bags, water in coolers, etc), get in the water (in a calm area) and measure it? After all, it's not like you're expecting some snow today, like we are in PA!

 

[Finest Kind]

Just keep an eye on the color of the water ahead, remember this, and you wont have to worry about your draft:

Brown, brown, run aground!"

That works in Bermuda but not so much in Jamaica Bay NY. At times all the water is brown and it is rarely blue

True, but Jonah posted from Nassau, and I'm assuming he is in the Bahamas, not in NY.