is adding a fuel tank 6ft aft of the bow on a 43ft monohull a bad idea?

[Brann-]

Hi,

Like everybody, I know that weight should be put as far away from the bow as possible. What I don't know is how important the effect is, particularly as you go farther and farther from the bow.

I think this is an interesting question from a theoretical standpoint, but in my case I've got a precise question in mind. On my 43ft 15 tons (33.000lbs) aluminium sailboat, I'm considering adding a big 300l (80 gals) fuel tank below the sail locker, approximately 6-8ft aft of the bow. I know it would be better to put it more aft, but it's not convenient, whereas the space I want to use is available.

Is it a very bad idea from a performance standpoint, or is it something that would barely be noticed?

Thank you!

[Alan Mighty]

Rule 2 of stowing is to keep heavy things (such as 300 litres of fuel) as close as practicable to the Centre of Gravity (CG) of the boat.

Do you know where the CG of your boat is?

If you do, you can use Rule 1 of Stowing. Which is to be mindful of the pitching moment of inertia contribution from each item or compartment. Another way of stating Rule 1 is "keep the ends of the boat light".

To calculate the contribution to pitching moment of inertia from your proposed fuel tank when it is full:

PMI = mass of tank x (distance from CG)^2

where ^2 means to square or to raise to the power of 2.

[JPA Cate]

Kinda depends on the hull shape, too. If she is narrow fore and aft, her shape will make her more prone to hobby horsing, than if her stern is broad. In the latter case, she will have some form resistance to pitching.

Try standing four men who don't mind being soaked on the foredeck 6 ft. aft, and then try to exit a barred entrance with wind against the tide conditions. If your boat pitches more than normal, or goes significantly more slowly than usual, well, there's your answer.

On edit: If trying the experiment above in the mind's eye gives you the answer, you won't have to share a slab of beer with them!

Ann

[Paul L]

If it's the only place you have the space for the additional fuel then make sure this is the tank you use first. It is probably no worse than the 8 Jerry jugs you see stored on the decks of lots of boats.

[StuM]

Originally Posted by Paul L

If it's the only place you have the space for the additional fuel then make sure this is the tank you use first. It is probably no worse than the 8 Jerry jugs you see stored on the decks of lots of boats.

It's the weight of 16 Jerry jugs. And Jerry jugs tend to b more spread out than a 300l fuel tank.

[a64pilot]

If you can’t get four men, a couple of 30 gl plastic barrels full of water will be close.
I bet you don’t notice it.
I believe some boats put their water tank">fresh water tank under the V berth as an example

[Paul L]

Originally Posted by StuM

It's the weight of 16 Jerry jugs. And Jerry jugs tend to b more spread out than a 300l fuel tank.

15, but who's counting? The deck jugs tend to be last used and stay full. They are also much higher off the water. A below deck tank can be first used. So, on avg it will have less of a negative effect.

I put a flex tank forward on My last boat - not as far forward as the OP. I always used it up first. It worked our well.

[boatpoker]

Call the designer and ask him.

[Brann-]

Thank you for your wisdom
Unfortunately I can't ask the designer because he's dead

as Paul L suggested, I'm planning on using the fuel stored there first, and possibly to leave it empty in most cases, that is unless I plan to go somewhere remote for an extended period of time (otherwise my other 100gal main tank is plenty)

Thank you !

[Suijin]

Well here’s some anecdotal experience. When I’m headed out on a long passage I will move 200’ of my chain from the bow locker to the main bilge. It makes a pretty significant difference in the motion of the boat.

[Panope]

Originally Posted by Brann-

........ On my 43ft 15 tons (33.000lbs) aluminium sailboat, I'm considering adding a big 300l (80 gals) fuel tank below the sail locker, approximately 6-8ft aft of the bow...............

On my 34ft 7 tons (15.000lbs) aluminum sailboat, I did add big 340l (90 gals) fuel tankage approximately 6 ft forward of the stern.


During the 5 five years of mucking around with the boat in this configuration (the most fuel I have had in this location is 60 gallons) I have not noticed a difference in performance/pitching. I do notice a big difference in trim.

Steve

[Bill O]

If that is the only place you can put it, then fine. If/when you need the extra range, fill it up and see if it makes a difference. It probably won't cause much of a performance difference, but if it does, run that tank first/transfer to the day tank before you tap into the other tanks. Problem solved.

The internal tank beats jerry cans on deck any day!

Bill O.

[Terra Nova]

Originally Posted by Brann-

...I know that weight should be put as far away from the bow as possible...

No! If that were true you could really load up the stern. Keep excess weight out of the ENDS of the boat.

Rethink this plan. Put additional weight down low and over the keel, as much as possible.

[Cheechako]

I wold say not too big a deal on that boat, but it is a big tank you are talking. Do you really need that much? I added two tanks to a cat I had, after leaving cruising, I realized I didnt need them at all , drained and left them empty. Also: Too much storage = old fuel.

[Brann-]

Originally Posted by Cheechako

I wold say not too big a deal on that boat, but it is a big tank you are talking. Do you really need that much? I added two tanks to a cat I had, after leaving cruising, I realized I didnt need them at all , drained and left them empty. Also: Too much storage = old fuel.

Well, I currently have around 100 gals, which is plenty for sailing in Europe, but I'm considering going to Patagonia, in which case I'll definitely need way more. It's not uncommon for boats sailing in those remote areas to have over 250gals of fuel in their tanks.

If possible, I'd like to avoid storing jerrycans on the deck, which seems to me as downright dangerous in high latitudes, and adding an extra tank closer to the center of the boat would be at the expense of storage space ...