Water tank capacity/yacht stability.

[coopec43]

I very much appreciate these forums because there are a lot of knowledgeable people willing to share their expertise. (But then, sadly, there are the "others" who just think they know........)

Currently I have three 40 gallon (200L) water tanks buried down in the keel but now I've decided to install a water maker with a capacity of 21gph. I am wondering what a sensible tank capacity would be?
https://www.ebay.com.au/itm/21-GPH-W...53.m1438.l2649

If I left the tanks in and filled them with water it would add to the yacht stability but if I took two out and replaced them with 300kg (660lb) of lead, the yacht would be more stable and I could then store heavy items such as anchors low down in the keel.

I would appreciate any advice from skippers of Cruising Yachts who would be qualified to comment.

[steve77]

Are you concerned about stability with your boat? I understand that adding more ballast will make her stiffer, but are you trying to correct a stability problem or just considering making her stiffer?

As far as water tankage goes - if I was cruising somewhere that I needed a water maker to supply drinking water, then I would not reduce tankage. If you are going to be someplace that has a shortage of drinking water, then I'll guess they also have a shortage of water maker spares in case you have a failure. Keep your tanks, and keep them full in the event of a loss of your watermarking capability.

A nit - you say you have three tanks, each 40 gallons/200 liters. What kind of gallons? In the US, 40 gallons is 150 liters and Imperial gallons are closer to 180.

Cheers!

Steve

[coopec43]

Thanks Steve.

I guess because I have a heavy mast section I am trying to make the yacht stiffer? (My Rigger/Sailmaker advised I should use lead ballast rather than iron). Does that answer your query? Stiffness or stability?

US gallons or Imperial gallons? I'm not sure: I'm guessing on the capacity as they are an odd shape. (There is actually three tall tanks)

As far as water is concerned I would always carry bottled emergency supplies of water (but we would have to go without showers for a few days).

Thanks Steve
PS Yours is a beautiful looking yacht!!

[gmakhs]

I would keep the tanks , I would have them empty when coastal and full when remote (with occasional top up from.the water maker ).
Putting all the heavy staff down there is not gonna improve a lot since the wait is high, and in a case of a knockdown or capsize imagine what can happen .
I do cruise with 250 litters without water maker and I always wish I had more .
I do believe water maker is not good to dink die to lack of minerals (though is safe to drink )

[coopec43]

gmakhs thanks for that.

Keeping the tanks in place even if empty most of the time is something I had considered.

However the keel is f/g and all ballast is internal. Once I have the yacht trimmed I'll pour epoxy around the lead billets and then epoxy/fiberglass the ballast in so it can't move in the event of a knockdown or capsize. If I put the anchor down there it would sit on top op the ballast and be shackled to one of the "ribs"(?) so it could move. (Probably the anchor would be within 18 inches (45cm) of the bottom of the boat so it would be well down low.).


Thanks for your help.

[HankOnthewater]

Ahum......., I haven't got certificate as a cruiser. Let me know where I can order one, online would be best for me. My avatar says I have boat suitable for blue water.......does that qualify me to comment? If you think not, go directly to the next post.

I have sailed several of Roberts Mauritius and its close sisters, both in steel and fibreglass, most of these over weeks at a time, or 500+ Nm trips. I cannot recall any difference if the watertanks were full or not, expect maybe floating a little higher. Most of these Roberts are home-built and offer a very wide range of fitouts. Therefore may I suggest, before you do anything else, to physically measure how much each tank can hold. You may find that the 40 gallon per tank is 30 or 50 gallon.

I agree with the previous posters, to leave your current watertanks in situ, that is if you plan to cruise for weeks at a time. Watermakers are not renowned to be ultra reliable. I don't know, but I guess breakdowns occur often, maybe not as often as autopilots and fridges.
Count on it that your watermaker or electric pump, or batteries or genset will fail to produce water at one time, or you run out of filters. Base your decision on how many people for how many days can live on the water in 1 or 2 tanks only. 160 litres for 4 people? Is that 4 days without a shower? Or 8 days severely rationed?

I am sure your boat's stability doesn't depend on tanks (water and fuel) being full. If it did, then at the end of each trip one would have a dangerous boat. However if the tanks are well below the waterline and central, I guess the boat would be a bit stiffer with full tanks, but we are talking about 4x160=640 kg or so. what is the displacement of your boat? 15 tonnes loaded if it is steel? And at the same time empty tanks reduce wetted surface and the boat would sail faster?

And if you were to take one or two tanks out, how easy is it to fit a 35 or 50 kg anchor there, and how easy to bring that anchor on deck in a raging storm? Certainly no large boat (stability) would depend on that kind of weight.
Although I am sure 160 kg of lead low, instead of 160 litres of water higher up would be better, but at times you may need the water.

My bias: I have a watermaker, and I have big tankage, and I have no intention to make the watertank any smaller. And my BIG anchor is on deck.

Edit: on re-reading, iust noticed you boat is fiberglass

[coopec43]

Thanks Hank for taking the time to respond

"Therefore may I suggest, before you do anything else, to physically measure how much each tank can hold. You may find that the 40 gallon per tank is 30 or 50 gallon".

But so what if they are 40/50 or 55L? The tanks are as big as I can get down the keelso I can't go any bigger: that's what I'm stuck with.

If I place the 40KG (60lb) anchor on deck that will be about 8ft (2½ M) above the Center of Gravity(?). As the ballast is about 3ft (1M) below the Center of G that anchor on the deck reduces the ballast by 8/3 X 40KG = 100KG. If I drop the anchor down on top of the ballast that will be a further 40KG of ballast meaning I'd be 140KG better off.

"guess the boat would be a bit stiffer with full tanks, but we are talking about 4x160=640 kg or so"

The designed ballast is 4000KG so 640kg is quite significant.

I'm taking on board your comments about water usage/crew and possibility of breakdowns. I'm about to "watch" the F1 Race on my computer so I'll go over your post again tomorrow.

Have a good evening.

Cheers

[sailorboy1]

I would keep the tanks and go cruising to see how it all works out for ME. Then I would know the answer for ME. Not trying to be flippant, just that the only one that matters is you and how you cruise/use your watermaker and tanks. The peanut gallery isn't really going to help you.

But, unless you have already proven to yourself you don't need the water tanks I wouldn't remove them.

[coopec43]

Sailorboy

The "Peanut Gallery"? Yes there are a few people posting here that reckon they know it all and are intolerant of anyone with different views (I wish we had an IGNORE button which some forums have)


As always a very sensible comment.
Thank you!

[Psy at SEA]

I may not be qualified to comment, but i suggest you leave the tanks in the boat.

I have a 55gl/hr watermaker with water tankage totaling 1600ltr ~ quite integral to ships stability.






Think Ill go take a nice hot shower.

[TrentePieds]

Quote: "...the yacht would be more stable... "

Precisely why are you worried about stability? I think that few of us are qualified to second guess Bruce Roberts in regard to the stability of his designs. You can make this 13 ton boat STIFFER if you chose, but that is NOT synonymous with making it more "stable".

There way be merit in making stowage space for hardware, such as ground tackle, where you presently have storage space for water, but doing so is not likely to have a significant impact of the boats "stability".

TrentePieds

[sailorboy1]

Originally Posted by coopec43

(I wish we had an IGNORE button which some forums have)


As always a very sensible comment.
Thank you!

there is, but you have to be strong on the web version not to still view a post

[MJH]

Originally Posted by coopec43

I very much appreciate these forums because there are a lot of knowledgeable people willing to share their expertise. (But then, sadly, there are the "others" who just think they know........)

Currently I have three 40 gallon (200L) water tanks buried down in the keel but now I've decided to install a water maker with a capacity of 21gph. I am wondering what a sensible tank capacity would be?
https://www.ebay.com.au/itm/21-GPH-W...53.m1438.l2649

If I left the tanks in and filled them with water it would add to the yacht stability but if I took two out and replaced them with 300kg (660lb) of lead, the yacht would be more stable and I could then store heavy items such as anchors low down in the keel.

I would appreciate any advice from skippers of Cruising Yachts who would be qualified to comment.

Leave the tanks in for more fresh water availability and management with the new watermaker. As someone posted, watermakers are notoriously, expensive, unreliable, and maintenance prone. I don't see any reasonable advantage to what you are proposing; after all it is a cruising boat not a racer.

I think it is important to know exactly what the capacity of your tanks are. One of the first things I did after buying my new-to-me boat was to make the effort to load the empty fresh water tanks one 5 gallon jug at a time, measuring the dip stick after each jug, then building a chart for them...they surprisingly turned out to be 2 x 100 U.S. gallon tanks. I've done kind of the same thing with my 2 x 75 gallon fuel tanks taking measurements before every fueling (one professional tank cleaning)and now have a useful planning chart. I refer to both charts often.

In planning for a 2016 Washington to Hawaii cruise, fresh water capacity and projected use for our crew of four was of major interest and crew management policy...you can't have too much fresh water on a passage.

~ ~ _/) ~ ~ MJH

[MartinR]

Keep the tanks. Increasing stability is often not what you want. Increased stability means an increase in performance, but also a decrease in motion comfort.

For a good cruising yacht there has to be a balance between these, and I am sure the designer of the yacht has accounted for this.

Also, an increase in stability will increase rigging loads, probably not significantly in your case.

[AndyEss]

Go for both, add some encapsulated lead for stabilityand switch your rigid tanks for flexible tanks.
I have 2 x 200 l flexible water tanks in my bilges and am happy with their performance.
I wouldn't rely on perfect and continuous water maker performance, but would want adequate water storage at least for drinking on the longest expected passage.