A technical battle of a Beneteau Cycledes or Oceanis 43' vs 38' sail boat

I'm trying to get a sense of physical difference between 38 and 43 Beneteau Cyclades yachts, but similar numbers are true for Ocanis series. I think the 38' is comfortable enough to live on for 2 people, but living comfort is just one piece of the puzzle. This article is written written so even non-yachters (like myself) can understand it.

Beam: 

Beam: 14ft 5" vs 13 ft 0"

The "beam" is the width at the widest point, look at 'b' in this daigram.

So the 43.3 is 1 foot 5" wider. Another way to look at it is it's 10% wider at the widest point. Big difference. As you move between the bow and stern, squeezing through the tighter places, on the 38' the smaller areas are 10% smaller, which will be noticeable. 

Length: 43ft 3" vs 39ft 4". 4 ft difference, or, 10% longer. Big difference.

Maximum draft: 6ft 2" vs 6 ft 0". 4 inch difference, or, 3% deeper. Not a big difference. You will not get any more access with the 38' hull.

Draft is the depth at deepest point below water line (look at 'd' on the diagram). Deep heavy keel means more stability in bad weather, but, it means you can't go very close to shore or into shallow areas.

Displacement: 15642lbs vs 22,005.9lbs. This is the weight of the water the hull displaces when it's submerged. Or, another way to think of it, if you were to fill the hull with water, and weight the water, this would be the weight.

Of course displacement goes up the more the boat weighs.. so if you load it up with fuel, fat people and huge tuna fish, it will sit lower in the water, and displace more.  The number they give is probably when it's totally empty, not sure. But the important thing is it's consistent. 

So we have difference of 6363lbs displacement or 28%! Interesting how non-linear displacement is. It's like airplanes. You add 10% length, but the boat weighs 30% more.

Higher displacement has pros and cons.

-When under engine power, you are moving 30% more weight, so, you will burn about 30% more fuel. That's a lot! It also means you need 30% larger fuel tanks just to go the same distance.

Engine: 40hp vs 54hp
See manual for Yanmar 3JH4E   

Fresh water: 87 gallons plastic vs 160 gallons. If we drink a gallon a day each, and use a gallon a day each for other stuff, thats' 4 gallons a day. So we can go 40 days on water supply in the big boat. Or 21.75 days on the small boat.

It seems enough in either case.

Fuel tanks: 58 gallons vs 52 gallons. Strange they don't put more fuel on the bigger boat, this limits range and how often you have to buy fuel. Fuel can be cheap some places expensive others so you want huge fuel tanks so you can fill up at a cheap place and wait until another cheap place to refill.

Motor cruising speed: both 7 knots

I found the manual for both engines and compared fuel burn to see if my gut instinct was right.

fuel consumption @ 2250rpm:

3.5 gallons vs 5gph

So yes, I confirmed the 43' burns 30% more fuel to go the same speed.

But I don't know how much we will use the motor, maybe not too much.

We can look at BVI marine diesel cost 2016, http://www.globalpetrolprices.com/British-Virgin-Islands/diesel_prices/

Right now it's $3.29 U.S. Dollar. 

So we will use $16 an hr vs $11.515 an hour for fuel.

I don't think it makes a huge difference for fuel cost in this case, these motors are amazingly efficient.

Sailing speed and comfort comparison

I compared the 38' and 42' Oceanis series (don't have data for Cyclades).

Sail Area to Displacemen is the important number. This is the equivalent of a car's power-to-weight ratio. We can see the 42' 19.5 vs 16.3 about 17% faster. So if you're doing an Atlantic crossing that takes 14 days in the 42' boat, it will take 17 days in the 38' boat. That's a huge difference in my opinion.

Surprisingly the comfort measure is almost the same, but, I did not research how this measure is derived.

Performance Comparison

LOA	Beneteau 373	36.92
	Beneteau 423	43.17
LWL	Beneteau 373	32.83
	Beneteau 423	38.58
Beam	Beneteau 373	12.33
	Beneteau 423	12.915
Displacement	Beneteau 373	14550
	Beneteau 423	19400.5
Sail Area	Beneteau 373	607
	Beneteau 423	881
Capsize Ratio	Beneteau 373	2.02
	Beneteau 423	1.92
Hull Speed	Beneteau 373	7.68
	Beneteau 423	8.32
Sail Area to Displacement	Beneteau 373	16.3
	Beneteau 423	19.52
Displacement to LWL	Beneteau 373	184
	Beneteau 423	151
LWL to Beam	Beneteau 373	2.66
	Beneteau 423	2.99
Motion Comfort	Beneteau 373	23.07
	Beneteau 423	24.65
Pounds/Inch	Beneteau 373	1446
	Beneteau 423	1780

Advantages:

the 42' boat is 17% faster, and has more room 

The deck is 10% wider which will make it more comfortable walking back and fourth.

Disadvantages: Burns more fuel, but fuel burn is cheap enough it doesn't make a huge difference.

Costs more, about $8k or 10% price difference for a 10-15 year old boat.

Verdict: Big boat wins on speed alone. Nobody wants to go 17% slower, everyone wants to go faster.