New water tanks placement

[mait]

Hello,

Asking for advice about water tanks placement for the OE36 sailboat I'm refitting.

The volume I'd like to have is 100...120litres (enough for my cruising).

Backround -
The boat is stripped empty so there are different options.
I am repowering with an engine that is 20kgs lighter than the original VP.
There is already a 110 litres volume HDPE fuel tank behind the engine under the cockpit sole.
I have 2x55L rectangular Plastimo bladders that I can use but not limited to those.

OPTIONS to place the new tanks:

A. 2 custom made HDPE tanks, 60litres each. Positioned aft from the engine, on both sides of the fuel tank, in the bottom of the hull. One under the quarter berth and the other in the bottom of relatively deep cockpit locker. Symmetrically positioned.
Pros: The best use of space that is hard to use for storage (hard access underquarter berth and deep cockpit locker). Therefore my preferred option.
Cons: Too much weight aft with all tankage there? (120l water + 110l diesel) Is that really a concern on a 7ton boat?

B. 2 bladders, 55litres each. Positioned under the port and starboard settees in the main cabin.
Pros: The best option considering weight placement. I already have the bladders.
Cons: The bladders do not fit so well under the settees (the boat is narrow and space there is limited). Lots of easily accessible good storage space is lost if I put bladders there.

C. 1 Triangular 75L tank in the bow, and 2 x 20L cans anywhere I can fit them.
Pros: Tank is available for reasonable money compared to custom HDPE tanks.
Cons: Weight will be in the bow area (there will be 15...18kg anchor up on the bow platform and 60metres of 8mm chain in the anchor locker up front, and the boat has long overhangs). Also easily accessible storage space in forecabin under the V-berth is lost.


I was really keen with the initial aft tanks idea because it gives the best use of storage space. But as I said, I'm worried about the weight.
Your opinions please?



Thanks and fair winds!

[Orion Jim]

I would go with option A. Your ground tackle will go a long way to offset the weight aft. Anchors and chain should be considered your life insurance policy, simply stated, more is better.

[Rucksta]

Empty the existing tanks and place crew two small crew members in the proposed locations and see how the trim works out.

[mait]

Originally Posted by Rucksta

Empty the existing tanks and place crew two small crew members in the proposed locations and see how the trim works out.

Thanks for the idea. That would be easy but the boat is on the hard, stripped empty in the middle of the refit and I have to decide the tanks placement to continue the work

[Rucksta]

I went with option A
400 lts just aft of BMax.

OEM was option B

Full tanks & anchor gear forward, short-handed crew give about the same trim as 100 lts midship tanks and a race crew.

It's only 100kgs.
If it's too much run the tanks partially full

[Bowdrie]

Is it possible to do a variation of option B, but using fiberglass to make the tanks integral to the hull?
A significant gain in capacity, while keeping the weight amidships so that the
fore-an-aft trim will not be affected.
Much to recommend if doable without undue effort.

[Cyrus Safdari]

Originally Posted by mait

Hello,

Asking for advice about water tanks placement for the OE36 sailboat I'm refitting.

I was considering building integral tanks under the settee but I decided to use the bilge. I have a centerboard so the bilge is divided in half, and each side will be a separate water tank. This puts the weight as far low as possible while also forming a watertight compartment if I should go over a reef one day.
There is still enough space in the bilge and under the engine to still serve as a bilge sump and to fit two large bilge pumps
Im not sure what the 2 tank volumes will be once done and this is probably not as large a volume as under the settee but that's OK too because my watermaker has a large production capacity, and has to be operated at least once every few days so there's no need for a large water tank

[wyb2]

Originally Posted by mait

I was really keen with the initial aft tanks idea because it gives the best use of storage space. But as I said, I'm worried about the weight.
Your opinions please?



Thanks and fair winds!

We had a Catalina 36, which is a very similar size and displacement, and looks to have reasonably similar proportions. We had 45 gal (170 ltr) between 2 tanks very close to what you show as option A (we had a 30 gallon near centerline and a 15 to starboard)

Maybe better sailors would have, but we never noticed a difference - in trim or performance - between full tanks and mostly empty tanks. I wouldn’t worry too much about the weight.

[mait]

Thank you for the ideas so far!

Built-in fiberglass tank is something I've thought about that but don't feel comfortable with.

I forgot to mention - there were (and will be) convectors/radiators for water based heating system under the settees making Option B even more complicated (there's even less space available).

Tanks in the bilge would be nice but I don't have much space there either because I need access to keel bolts.

I think option A is the way to go, and if the trim will be too bad then rearrange.

[Carlos M]

Originally Posted by mait

Thank you for the ideas so far!



Built-in fiberglass tank is something I've thought about that but don't feel comfortable with.



I forgot to mention - there were (and will be) convectors/radiators for water based heating system under the settees making Option B even more complicated (there's even less space available).



Tanks in the bilge would be nice but I don't have much space there either because I need access to keel bolts.



I think option A is the way to go, and if the trim will be too bad then rearrange.

Can’t opine on the weight placement but what about flexible bladders in the aft positions? Instead of custom HDPE? I am going to add a bladder to my OE HR Mistress 32 under the SB quarter berth. Sort of compensated by the starter battery and a ton of assorted stuff in the port side deep cockpit locker. My main water tank is PE triangular under the V berth but too small for the intended purpose and the space under the quarter berth is indeed very hard to access.

Ps: enjoyed your videos about the bringing your boat home and the gigantic job on the keel!

[mait]

Thanks Carlos! That's probably the best approach as I already have the bladders.
I can build the quarter berth and cockpit locker so that I can swap the bladders for HDPE tanks later, should I decide so.


PS the job on the keel was not so gigantic considering all the other work ahead of me. But I'm making steady albeit slow progress

Originally Posted by Carlos M

...what about flexible bladders in the aft positions? Instead of custom HDPE?
...
Ps: enjoyed your videos about the bringing your boat home and the gigantic job on the keel! ...

[wingssail]

I installed custom built tanks under the settees in my boat (fuel and water, 4 tanks total in that location). I would be surprised if you couldn't get much more than 55lt (14.5 gal). I installed 25 gal water and 30 gal fuel under each settee in aluminum tanks build to closely fit the available space.

One advantage of the water tanks in this location is that you can use them to fine tune the balance, side to side, of the boat.

Another is that the fore and aft trim does not change as tanks are emptied or filled.

But in my case I needed more water and I also installed two additional water tanks aft of the engine, 45 gallons each, side by side, for a total water capacity of 140 gallons. (remember that this was before wide use of water makers).

The aft tanks are triangular and the volume is concentrated at the forward end, yet still, it was over 600lbs placed aft but when cruising we did not notice any change in trim or performance. However, since my engine is in the center of the boat, not aft as is yours. My aft tanks are not placed as far aft as yours are proposed. While racing mine are all empty.

All tanks can have individual filling pipes and individual shut off valves to keep the water separated and to keep the water from flowing from one tank to another when heeled.