Topic: Question re: boat trim and balance

Any idea why JJT put the water tank in the bow and the holding tank in the bilge?  With a load of water on, Virago sits well down by the bow, even with the engine, a load of diesel and me in the back.  The only reason I can think of for this arrangement is to counterbalance the weight of the engine to even out the weight distribution and centralize the CG.  However, it does seem odd that she trims below her lines when water is topped up.  Has anyone swapped these tanks around to move the weight of the water aft?  Does it make the boat light in the bow, or particularly heavy by the stern?  I'm toying with the idea of moving the water storage but am afraid that I'll screw up what is currently a well balanced, easy riding boat - except for the load o' water thing.

Re: Question re: boat trim and balance

If the water tank is ten gallons, empty your tank and take eighty pounds of weight and move it fore and aft in the boat to see how this effects trim.
In my refit I'm planning on using flexible tanks, perhaps wine bladders, to hold water in the bilge, in the bilge where the holding tank was, but won't be any more as I have pulled all the plumbing and am going for a porta-potti. I don't want my potable water in a f/g tank . . . .
The water in tank in the bow also serves as a watertight crash zone (excuse the terminology). With any kind of luck this watertight bulkhead, of sorts, might keep the boat a float if you should hit a log at night.

Re: Question re: boat trim and balance

I have the holding tank forward under the V-berth, with a 15 gallon water bladder above it. I have another 15 gallons of water in the side storage area at the aft end of the V-berth. Right now they are empty. There are 5 sails and a zodiac in the v-berth. The rest of the boat is empty of the usual extended cruising gear and supplies. In the aft I have a Yanmar 1GM10, 45 liters of fuel, 75W solar panel and a monitor windvane. In this state she sits well down is the back with 5 inches of the bottom paint at the bow above the water. When she has a full cruise load, she sits almost level, but well down of coarse.

Re: Question re: boat trim and balance

huh.   How much weight does your windvane and large panel add to the equasion?  With an empty water tank, our boats are loaded similarly for day sailing - sails up front, engine and related stuff in back - and Virago sits pretty level.  I wonder how different our boats are, in model year and also placement of waterline and boot top stripes.  Something else to consider is that I've always been on my boat when sailing, so I've never seen her sail, so I don't know how much she squats when underway - if at all.

Re: Question re: boat trim and balance

The windvane is 95 lbs and the solar panel about 25. Then there is the extra anchor, chain, line and lots of spare line. Now that you remind me I did move up the boot stripe and bottom paint, but I probably moved it equally front and aft. But I was just judging from the visibility of the bottom paint. I should pay more attention to the other details like deck angle.  Maybe I will put a level on the cabin and cockpit soles.

Re: Question re: boat trim and balance

I don't think I'd get that particular!  I'm not gunning for dead level so much as I don't want to muddle up the physics of the hull too badly.  There's a good article in Good Old Boat this month on what makes a boat seakindly.  That's what I want to protect in my boat - her good manners and seakindliness.  Thanks for the feedback and thoughts though, it's good to think "out loud" sometimes.

Re: Question re: boat trim and balance

I can comment on the original question.  On my 1976 Contessa the holding tank is under the V-Berth and the water tank is (was!) in the port quarterberth.  The attraction of the holding tank in the bilge is that black water from the head flows downhill and clears the lines.  Where my holding tank is forward, I must pump uphill to pass fluids into this tank, so there is always sewage in the hoses from the head.

Ironically, I picked up a Plastimo bladder tank last season, with the intention of placing it beneath the cabin sole.  In effect, my fresh water will be right on the centre of gravity and the holding tank (which should rarely be full) remains forward.  I have not yet tested this arrangement as I am tied up in Guyana this season, but I will let you know if it proves to be a mistake.

Cheers!

Re: Question re: boat trim and balance

After reading this thread and preparing to Awlgrip my boat this fall/winter, a boat which I've not seen in the water, I would like to ask all about how the stock (factory)  waterline may compare with the actual waterline.
I'm going to repower with a slightly heavier motor, probably a Beta, and install a windvane. The Awlgrip cannot be in the water and therefore I may need to raise the waterline accordingly. My boat has a double boottop which I plan to elimante in favor of one.
Tell us your waterline stories . . . . .

Re: Question re: boat trim and balance

i took the waterline up to the top of the gelcote stripe, and in the water not loaded up with much she has about 3" to go before hitting this mark

Re: Question re: boat trim and balance

Stefan,
Did you have a double or single boottop?
I've seen a number of these boats with a single boottop. I don't know if the double stripe was an option or that owners just eliminated one in favor of two because of ease of painting.
Either one or two I understand you just brought the bottom paint up and over the boottop to meet the topside gelcoat. Do I have that right?

Re: Question re: boat trim and balance

I'd like to hear how your experiment turns out Christopher.  And I hadn't thought about the drainage of the head as I don't use my head - but that is a good point.  Also, the water tank lightens up with use, unlike the holding tank if it's used.  I wonder how the long distance Contessa sailors pack their boats and if they pay any attention to trim and balance.  I've loaded mine for 4 weeks on the Great Lakes, but I'll bet that's different from loading her for 8 weeks in blue water.  For rbporter - the lines on Virago are original to the boat - an '85 JJT.  So far they seem to be well placed - the waterline is at the waterline stripe of a lightly loaded boat, down slightly by the stern due to the engine (original Buhk diesel), but the boot top is still dry.  The boot top becomes the waterline when she's loaded, but the full load of water that got me started on this topic puts the boot top under at the bow, but I think that's a load distribution puzzle more than a function of the lines.

12 (edited by stefan_d 2008-09-02 15:52:52)

Re: Question re: boat trim and balance

when i painted the topsides, i painted to the top of the single bootstripe and then when i did the interprotect bottom i brought it up to the top of the bootstripe.

the bootstripe had been previously painted over with antifouling leaving me to believe that once loaded, she sat a bit lower than intended.
this weekend i can shoot some measurements from hull deck joint to painted waterline if you like

just uploaded the newest picture of the boat and you can see the blue / black.  the black is where diana had painted with antifoul so i interprotected to there.  the black that is out of the water is pretty much 3/4 of the original waterline stripe.

Re: Question re: boat trim and balance

Further thoughts re: position of water tank in later models....Maybe it has nothing to do with balance and more to do with how JJT re-worked the boat.  From what I can read, JJT lowered the floor in the boat to increase the headroom, which may have crowded out the original water tank.  Perhaps they moved the water tank to the bow in order to keep the tank volume suitable for longer distances.  Regardless,  a full tank still puts my boat down by the bow.  The soft tank under the floor solution may work because it makes use of what little room there is below the cabin sole.   I believe Varuna had the water tank moved to a position under the floor at the time of construction - do we know if the holding tank was used as a water tank, or if a different tank was installed?

Re: Question re: boat trim and balance

WHen my engine was out for repairs in Rhiannon, I had to put a note on her saying "thank you for noticing her bow is lower than her stern, but she is not sinking, she has her engine out', as everyone noticed the bow was noticeably lower when the engine was out, so it is definitely about trim...try putting all your tools on one side, you will notice! ;-)

The are narrow, little boats: you can have them list with two people on one side...but you can't push 'em under, lol

“You get a boat for only one reason, because you want one.  If you’re worried about being practical, forget boats.”

Re: Question re: boat trim and balance

Since I repowered with a Yanmar 1GM10, my contessa is down by the bow a bit because the original Aurona diesel was 100 pounds heavier.
Also my 18 gallon black water holding tank is in the bow. I can tell when it's full because water stands on deck after a rain because the deck drains are well aft.

The cutworms are in the hollyhocks, again!