Boat size?

[tuffr2]

When I think I may win the lottery I look at boats. I always want to look at the largest ones at the boat shows. Like a moth drawn to the night light.

Anyway my question is a 40 foot boat twice as big as a 30 foot Boat? And 50 foot twice as big as a 40 foot? And 60 foot twice as big as 50 foot?

It sure seems that way.

[danielamartindm]

The relative interior volumes of 40 and 50 foot boats will vary with design, but what you've noticed is very true- a few added feet of loa translates into huge differences in interior space- we're talking about area, and as length increases, so generally does width.

[Kenomac]

Yes it's true, look at the displacement.

[tuffr2]

My knee jerk though has always been a 60 foot boat is twice a big as a 30 foot boat...my mistake is using length and not volume or displacement.

[StuM]

VERY roughly. If you just scale directly up, volume is the cube of length

So every 10% increase in length would approximate to a 33% increase in volume (1.1 x 1.1 x 1.1)

30 - 40ft = 33% increase = 2.35 times the volume
40 - 50ft = 25% increase = 1.95 times the volume
50 - 60ft = 20% increase = 1.73 times the volume.

[tuffr2]

That is kinda what I was sensing when I walked on different boats. I came away thinking there was a huge difference between 30 foot and 40 foot but a lesser difference between 50 foot and 60 foot.

Thanks for the formula.

[geoleo]

Originally Posted by danielamartindm

The relative interior volumes of 40 and 50 foot boats will vary with design, but what you've noticed is very true- a few added feet of loa translates into huge differences in interior space- we're talking about area, and as length increases, so generally does width.

Speed also increases dramatically with more length

[Pizzazz]

Unfortunately, speed does not increase "dramatically" with length as it is governed by the square root formula. If your waterline increases from 25 to 36 feet (45%), you speed increases by only 20% which is hardly dramatic.

Also, note that while the volume does increase as the cube of length in the middle of the boat, larger boats typically need a finer entry and exit (or swim steps), so you do not get the full benefit. Pretty much all boats in the 30-40 foot range have a similar size main cabin but you get more storage and bigger sleeping/showering areas. Also a much larger cockpit if aft cockpit.

My advice would be to think about how you use the boat first. For example, the other day I had 14 people on my 31 footer, half of them not really sober. It was OK for a midnight sail. However, if two people need to spend one week cruising on the same boat, it will be tight because of the lack of storage.

[geoleo]

Originally Posted by Pizzazz

Unfortunately, speed does not increase "dramatically" with length as it is governed by the square root formula. If your waterline increases from 25 to 36 feet (45%), you speed increases by only 20% which is hardly dramatic.

Also, note that while the volume does increase as the cube of length in the middle of the boat, larger boats typically need a finer entry and exit (or swim steps), so you do not get the full benefit. Pretty much all boats in the 30-40 foot range have a similar size main cabin but you get more storage and bigger sleeping/showering areas. Also a much larger cockpit if aft cockpit.

My advice would be to think about how you use the boat first. For example, the other day I had 14 people on my 31 footer, half of them not really sober. It was OK for a midnight sail. However, if two people need to spend one week cruising on the same boat, it will be tight because of the lack of storage.

If you used meters instead of feet it would be more "dramatic" and 20% faster is huge when dealing with slow sail---boaties