Building a TUG

[marshmat]

Hi Eric,
A quick note about weight estimates. While the hull itself is a pretty big contributor, don't forget about engines, gearboxes, rudder gear, batteries.... and of course interior furnishings, doors, windows, stairs.... then there's cookware, appliances, foul-weather gear.... stuff really builds up. It's amazing just how much weight can be added to a boat through random stuff that you don't think of while designing. A 6-tonne hull, with a design displacement of 10 tonnes, has only four thousand kilos available for everything else- machinery, people, gear, etc. Getting the weight estimates accurate can save a lot of grief later.

[Barbaros]

Hi Matt,

Thanks for this precision. I was more vorying about the "ballast" and how to add some more weight to reach the required draft. But, I think you are right.
Still, the draft (sinking the propeller to an acceptable depth) appears as more problematic then the rest.
Even a steel hull remains very light.
For exemple, Rhino shows 20 tons ( 20 000 X 2.2 = 44 000 pounds) for a draft of 1 meter (39 inches). All surfaces togehter including the windows (!) in steel weights only 7 or 8 tons (17 600 pounds) which is very light compared to 44 000 !!!.

Regards
Eric.

[marshmat]

Remember, it's always easier to add ballast than to remove inherent structural and machinery weight....