External Water Ballast

[Snowpetrel]

Looks like a great way to add water ballast to a cruising boat. The performance enhancement (both to comfort and speed wise) would be pretty nice. I guess the real issues are around the details of pumping and securing the tanks, and the cost/benefit/ vs extra complexity side.

If I recall correctly they used to market a water driven pump to fill the tanks. Lower it into the water as you sail a propeller drives a pump to fill the tank quickly.

Other plusses would be filling it with air and water to make a great fender, transfering FW in bulk etc.

The concept is certainly very appealing. I remember a long distance french sailer who used to rig up his spinnaker pole and hang a few jerry cans of water off it on long tacks to improve his speed. he seemed to think it helped his shallow draught vessel enough to be worth the extra complexity.

Prehaps the bags could go on deck rather than over the side. Not as neat but more secure?

Cheers

[Snowpetrel]

Also be a good idea to get something in writing from Hunter about the maximum number of crew acceptable as rail meat, Weight to windward will add some extra loads to the rigging and hull, and you want to be sure the rig and hull can take it without insurance companies getting twitchy.

(waffle alert).. Though in reality the extra maximum loads will increase by not quite as much as at first you might think due to them loosing effectiveness at higher angles of heal so the maximum righting moment(RM) and RM30 (RM@30 degrees) will not increase by as much as the RM15 and most boats rigs are sized based on RM30 values. Effectively the rail meat (ballast bags) increases the power(RM) of the boat at a more useful heal angle, on most modern boats the maximum power(RM) occurs at stupid heal angles where it cannot be safely used, but still has to be allowed for in the mast calcs incase of gusts.

[Snowpetrel]

Originally Posted by FranklinGray

I guess the issues I'm worried about are:

1) The dynamic forces from the bag to the connection points.
Its just engineering, should be prettty simple to add some extra pad eyes and cleats to take the loads
2) Why I never see any other cruisers using them considering those who sell them claim it would be beneficial to any boat.
Most cruisers couldn't be bothered and motorsail in these sort of conditions
3) Would it make the boat out of balance and cause problems after a big wave has passed? I guess not because we are basically talking about rail meat used in racing, right?
No problems, as long as you are sensible. Of course getting caught with the ballast to leeward would not be nice, and using it downwind is not advisable, due to deep rolls to windward. It might even help ultimate seaworthiness by giving you the power to sail to windward in nasty conditions, and much more energy to capsize the boat.
4) I've know a few boats have used them in races but I haven't heard of many. If it works so well one would think all racing boats would use them, right?
Generally they are not allowed to use water ballast or are heavily penalised for it, whereas crew weight (and stacking any movable items to windward) is free speed, and is not penalised. Generally short handed boats more often have (and some need!) water ballast. It is often allowed in this case, subject to certain limitations. Nowadays canting keels are where its at, being generally faster if allowed

In light airs a leeward one can be filled to induce a slight heel, helping to keep the sails filled. at anchor with both filled the boats roll period would be much slower, if they where lowered half into the water they would damp most roll...

[UNCIVILIZED]

If you're going to do it, first find out what your RM30 is. And then do the math to make sure that the liquid ballast which you're adding, reduces the amount you're heeled by between 5-10 degrees.
Less than 5 degrees isn't worth the effort. And more than 10 degrees can be dangerous if you happen to get caught with your water ballast on the wrong side, accidentally. Or when you're letting gravity fill the new "windward" tank, just prior to a tack or jibe.

10 degrees is the max allowed by racing rules (as of last check) so that the water ballast isn't a large hazard to your stability, if you get caught with it on the wrong side.
And ideally, you'd have it integral to your boat in the form of fresh water tanks, but... that'd be an expensive refit.

Water ballast definitely works. It's just not quite so much in vogue now, as after a decade+ of teething problems, canting keels are the in thing. Due to boats being lighter, with better RM with them as compared to water ballast. Though it is still used, especially to alter fore & aft trim to greater benefit. Particularly on the big, short-handed racers.

BTW, if you're not keen on attaching things to the toe rail. And personally, I'd want it connected to several other structural points, myself.
It's fairly easy to beef up the deck laminate, & or structure also (meaning hull to deck connection), where ever the tanks will be going.

[FranklinGray]

Thanks all. Yeah, I guess if I was adding too much weight I can just empty some of the water. The makers talk about using different amounts depending on the wind conditions. As for having to tack, just have a pull string on the plug so you can pull the plug to empty it from the cockpit. As for filling them...no, I'm not manually pumping anything...that is why they made electrical pumps and yeah, I do remember years ago some company advertising a pump that is ran when you drop it in the water while sailing.

As for having to store them. Well, one idea is to just have one and put it on the side I feel I need it for the long tacks. Another idea is to just leave it on the side but that could be a problem when coming to the docks like fuel dock. Another idea is pulling them up on deck and slip into a Sunbrella bag and tie to the lift lines.

I'm not worried about the bags jumping around. My jugs don't jump around in the rough conditions. The weight will keep it down. As for waves hitting them...I think they are high enough that would rarely happen except when I let the water out and tack. Then even though deflated they would be in the water until I got the heeling under control.

I am glad I didn't read too much negative stuff on here to drop the idea. I think I'm going to give this a try if I can find a company I feel safe buying it from and I can figure out a way to bolt something down with a big enough backing plate system. That is always a challenge on these Hunters with their deck liner on the inside. Had to deal with that when installing a rain catching system to feed the water off deck into the tank under the V-birth.

Thanks again all and I will update this thread when I get around to doing this...I guess this summer when my travels slow down.

[UNCIVILIZED]

Here's a link which contains a good amount of info on Water Ballast, & links to yet more & even better (aka expert) info on the topic.
waterballast set-up for 40ish foot (almost) racing yacht - Boat Design Forums

[TeddyDiver]

The real issue would be the effects to stability. Adding some 1200lbs on the deck rises the CG about 4 to 5", this means for a boat of this size (I'm now making a some assumption becouse of the absense of the original numbers) the AVS to change from 140deg to120deg if not more. This is considered dangerously low AVS (angle of vanishing stability).

BR Teddy

[UNCIVILIZED]

Teddy, where are you getting data which states 120 degrees AVS is dangerously low? That & I doubt that the vessel in question had a 140 degree AVS to begin with. From many, many years of racing, & working with designers, plus reading polars, I know that there are a lot of boats out there which barely squeak by the 120 degree mark (if at all when loaded with cruising gear, furlers etc). And fewer that hit 140, although there are more now than in say the late 70's to early/mid 90's.

When water ballast became popular, the various racing regulatory bodies decided that water ballast couldn't alter a boat's trim/angle of heel by more than 10 degrees, so that if such a vessel got caught with the ballast on the wrong side, it wouldn't be in overly dangerous territory, stability wise.

And out of curiosity, how's having water ballast on the rail more dangerous than crew? I mean if it's in a bladder tank, 10sec with a knife & it's gone (faster if he uses QR shackles to secure it). Which is about as quick as you'll get half a dozen guys off of the rail.

[Snowpetrel]

Originally Posted by TeddyDiver

The real issue would be the effects to stability. Adding some 1200lbs on the deck rises the CG about 4 to 5", this means for a boat of this size (I'm now making a some assumption becouse of the absense of the original numbers) the AVS to change from 140deg to120deg if not more. This is considered dangerously low AVS (angle of vanishing stability).

The raised COG does reduce the AVS, but the extra stability at lower angles of heel more than compensates so in most cases the vessel will be much harder to capsize (more positive area under the RM curve) with the windward water ballast tank full, and also much greater roll moment of inertia. In addition it gives more power to enable a vessel to continue to sail to windward in extreme conditions, this can be an effective storm technique on a boat with enough power to maintain control.

But the OP is not talking about using it in extreme conditions, just to enable fast and comfortable sailing with the wind forward of the beam in stronger 20-30 knot conditions when the sea state otherwise can mike things very slow and uncomfortable, not extreme conditions.

[TeddyDiver]

Originally Posted by UNCIVILIZED

Teddy, where are you getting data which states 120 degrees AVS is dangerously low? That & I doubt that the vessel in question had a 140 degree AVS to begin with. From many, many years of racing, & working with designers, plus reading polars, I know that there are a lot of boats out there which barely squeak by the 120 degree mark (if at all when loaded with cruising gear, furlers etc). And fewer that hit 140, although there are more now than in say the late 70's to early/mid 90's.

When water ballast became popular, the various racing regulatory bodies decided that water ballast couldn't alter a boat's trim/angle of heel by more than 10 degrees, so that if such a vessel got caught with the ballast on the wrong side, it wouldn't be in overly dangerous territory, stability wise.

And out of curiosity, how's having water ballast on the rail more dangerous than crew? I mean if it's in a bladder tank, 10sec with a knife & it's gone (faster if he uses QR shackles to secure it). Which is about as quick as you'll get half a dozen guys off of the rail.

As I said I didn't have much of data except the beam, displacement, ballast (keel weight) and draft, so my figures are a rough estimate. Freeboard height would help some, but still just an educated quess.
Cruising gear as furlers, jerry cans, solarpanels and such placed high will outercome every ounce placed under the cabin sole, which is the only place for cruising gear contributing anything to increase stability. With flat underbody that isn't much.
Wonder how fast one could jump from the cockpit on to the side deck to cut the bladder when the boat is in a knockdown situation?

Snowpetrel,
Only for one direction, other one is compromised.

Anyway IMHO, better to get profesional help with the calculations before doing anything stupid

BR Teddy

[Snowpetrel]

Originally Posted by TeddyDiver

Snowpetrel,
Only for one direction, other one is compromised.

Very true, though as soon as the ballast bag goes underwater on the lee side it has no further heeling moment, just becoming drag. Certainly a plus for the external ballast bag concept over internal water ballast, but still not much fun!

Another interesting article in support of water ballast on a small cruising boat here. He also stresses your point about the effect of the raising of the COG, though at normal sailing angles this is not a important factor.

Cheers

[Ardbog]

Hello, does anyone have any specific experience with the maximarine type ballast bags or other similar ones?

Inparticular do you need a reinfoced gunwale to avoid damage if hit by waves etc?

Are there issues with them coming off?

Can you lower/parially submerge them to act as stabilizers at anchor or drougues (assuming one on each quarter)?

Thanks

[FranklinGray]

I can't answer your questions but I might be able to provide some info to make your questions a mute point.

Unless they have change their mind in the past 6 months, the company no longer has any bags in stock and is not going to make any more

I guess it just wasn't a hot seller item.

I don't need it anytime soon so that is ok. I"m crossing the South Pacific this year and that is mostly downwind sailing. Maybe in a few years I'll bring this thread back to life