How much does all your crap weigh?

[Hud3]

Our boat settled about 2.5-3" when we loaded it up for cruising. I'm told an inch is worth 1,500 lb for the IP 380 (39.9' LOA, 32' LWL, 13.2' Beam). 2,300 lb was fuel and water, and I'd say the rest was about 2,200 lb in equipment, spares, food and personal stuff.

[Gerrycooper56]

I'm with you - we have a water maker and 2 x 100g water tanks, no jugs. The aft water tank is filled from the water maker while the ford one isn't

Originally Posted by colemj

I didn't mean to imply that we start with no water and just make what we need on the way. I meant to imply that we don't need to have completely full tanks and extra jugs of water lashed to the rails. The watermaker will supply 30 gallons in an hour, which provides us with comfortable choices on when to run it and how long.

My point is that something that is considered in this thread a frivolous weight addition (watermaker) can actually leave your boat lighter on passage (and at all times, actually) because you don't need to carry large heavy stores of water. Just leaving 50 gallons out of the tank or out of the jugs saves almost 500lbs! You would need to throw off a lot of gear and provisions to match that.

Mark

[Nicholson58]

I used to race a Heritage One Ton long ago. We installed a large dock box and stripped off enough extras to raise the WL by nearly three inches. We left heavy sails in the box on light air days. This made a huge difference competitively in the range of 0.1 to 0.2 knots. That said, for cruising, I could not care less about 0.2 K. The present boat is massive. I see extra weight more as effecting how quickly we reach steady state speed rather than how fast can we go.

[Neptune's Gear]

I reckon your original estimate is a bit light! On our 40fter with 2 people, and all the cruising gear about 1200KG, excluding fuel and water. But we do carry a LOT of tools and spares - more than most. And all the normal stuff. Island Time is unloaded now, and came up about 5-7 cm on her lines.....

[El Pinguino]

Originally Posted by carstenb

Here's the formula for change in immersion with added load.


T = L*W/120 =[t/cm]
L*W = length (waterline) Xwidth (waterline), all in meters and decimal parts thereof [m*m]

Change in immersion
(Δ)dm = q/T [cm] q= added load in metric tons, T(cm) from formula above)

New immersion- dm,2 = dm,1 ± q/T*100 [immersion in meters and Load q in metric tons]

On our boat 12meters by 4 meters (I've just rounded off to make all this easier), adding 2 tons of load means:

T=12*4/120 = 48/120 = 0.4 (tons per centimeter of change in immersion)

2 tons therefore = 5 centimeters change in immersion

I've just revisited this thread...using 120 in the first line suggests a coefficient of fineness of about 8.33... sounds more like a VLCC than a yacht.

I think a CoF in the order of 0.6 would be more like it in the case of a yacht.

That would give in the example above ( 12 x 4 x 0.6 )/100 a TCPI of .288

So loading 288 kilos would sink the sample yacht by 1 cm. 2 tonnes would sink her 7 cms.
Still not a lot IMNSHO.
More info here for them as cares Stability

Anyone really wanting to know the waterplane area of their boat should use Simpson's Rules... Ship Stability for Masters and Mates - Bryan Barrass, Capt D R Derrett - Google Books

[carstenb]

Originally Posted by El Pinguino

I've just revisited this thread...using 120 in the first line suggests a coefficient of fineness of about 8.33... sounds more like a VLCC than a yacht.

I think a CoF in the order of 0.6 would be more like it in the case of a yacht.

That would give in the example above ( 12 x 4 x 0.6 )/100 a TCPI of .288

So loading 288 kilos would sink the sample yacht by 1 cm. 2 tonnes would sink her 7 cms.
Still not a lot IMNSHO.
More info here for them as cares Stability

Anyone really wanting to know the waterplane area of their boat should use Simpson's Rules... Ship Stability for Masters and Mates - Bryan Barrass, Capt D R Derrett - Google Books

You're right, of course. The coefficient can be chnaged to suit the type of boat. The formula I put up is the one taught in the Danish Yachtmaster Ocean. Obviously, anyone who is serious baout htis, should try it empirically to find the correct coefficient for their own boat.

Noté the waterline, add weight until the boat displaces 1 more centimeter, use the formula backwards and find the coefficient.