Sharpie water ballast

[Ignatius]

Hi everyone. On the verge of starting to build a Sharpie similar to the 18 ft NIS. According to stock plans a ballast ratio of 50/50 is required (Boat 300kg, ballast 300 kg roughly). The 18 ft NIS (or similar ballasted sharpies) seems to be the only 20 footish, really trailable (not just moveable) , shallow draft boats with adequate headroom, that is available. But, I need to bring trailer weight down, to below 1000 lbs. Hence studying partial water ballast as an option.

Question 1: What is the advisable ratio of water ballast vs lead ballast. Will 200 kg (400lbs+)water ballast and 100 kg (200lbs+) lead will be OK? (lead ballast will then the be the variable , for trimming the boat) Parker also uses lead/water combination in his sharpies, I have his book, but the ratio is not mentioned.

Question 2: The plans calls for two transverse lead sheets 3cm/1” thick, laid directly on the bottom. My idea is to reduce that to 1cm, bringing the weight of the overall weight of the lead down about two thirds, from 600lbs to 200 lbs. Problem: As you know it is not just about weight but also about position, CG, etc Will it be critical in terms of the CG to install water ballast on top of the thin lead sheet, in exactly the same prescribed position, still below waterline? We’re talking about 6-7 inches thick water tanks. (Design has a slight rocker)
The CG of the total ballast will thus not be directly on the bottom itself, but slightly higher, somewhere within the waterballast , I presume. Is this negligible or critical? Can I go ahead? Thank you

[Thorne]

Looks like you may be getting yourself into some serious re-design work here -- and if you've picked the design for "adequate headroom" you may find that this goes away after adding water ballast tanks. But if you like this sort of marine design work, you'll get a lot of good advice here.

There is also the whole thing of filling and emptying the tanks -- will you do it with just gravity/water pressure, or have manual or electric pump backup? You may find that you've traded off trailer weight for a LOT of pumping and draining...

At some stage it will be MUCH easier to get a larger tow vehicle...which I assume is your limitation here. Or build one of the boats designed for water ballast, like the SeaRaider and BayCruiser from Swallowboats in the UK.

http://www.swallowboats.co.uk/content/view/99/106/

[TerryLL]

The NIS boats may look like any other flat-bottomed, slab-sided generic hull, but the sailing performance, and especially the self-righting performance, are the result of some pretty sophisticated design work by one of the world's foremost designers. Before you go tinkering with the ballast, an inquiry to Bruce Kirby would be a smart first step.

http://www.brucekirbymarine.com/

[Ignatius]

Thank you Thorne and TerryLL. Maybe I should just explain that I’m not building a NIS sharpie (Just used it as an example cause it’s well known) I’m building a Sharpie600 www. bjornthomassondesigns.com. The hull dimensions are similar, but not the building technique, and not the rig, ballast arrangement, etc (and specifically not the looks also) I have the blessing of the designer to go ahead with supplementary water ballast, as long as the same CG position is used. So it is not about the merit of doing this, but the principles involved. Not tampering with a design here, merely trying to bring down trailer weight in an accountable way.

Thorne, the water ballast tanks will not interfere with headroom in any way, as it will be situated beneath the double V –berths, where the transverse lead sheet (from chine to chine, on bottom) will be placed - according to the plans. Headroom will remain 1.35 – 1.4 m. Will loose some storage below bunks, though, but that’s a small trade-off as I will not be circumnavigating J

And the tanks will be gravity filled and emptied ( Thanks to ‘Banjo’ building his John Welsford’s ‘ Sweet Pea’ and sharing his concept and photo’s on this forumJ )

So still I’m wondering: How do designers like Parker use the lead-water combination in Sharpies ? Next to each other? Water on top of thin lead sheet? Longitudinal and tranverse combination? (Talking internal ballast only, off course) Any ideas?

[JimD]

Lines for the Sharpie 600 (a little under 20 feet) http://www.thomassondesign.com/

http://www.thomassondesign.com/img/sharpie600bild3.jpg (http://www.thomassondesign.com/choosing/small_boats/sharpie_600.aspx)

http://www.thomassondesign.com/img/sharpieritning.jpg

Have you asked the designer? I would.

[Thorne]

Jim - He's asked the designer and gotten the OK, see above.

Ignatius -- I really think your are dreamin' if you think you can get this size boat with all the rigging, gear, equipment, water, etc **on the trailer at 1000lbs or less**. I have some experience here, as my San Juan 21 was spec'd by the builder at 1800lbs -- but set up for cruising she weighed over 2300lbs.

The designer lists this boat at 600kg, which is over 1300lbs -- but that is the basic weight without gear, water, etc.

Again, is the issue your tow vehicle?

[JimD]

Jim - He's asked the designer and gotten the OK, see above.



Oops, sorry, missed that. Thorne, looks to me like the designer has given the ok to something that is not possible. He says yes to water ballast but only as long as it doesn't change the Centre of Gravity:
I have the blessing of the designer to go ahead with supplementary water ballast, as long as the same CG position is used

How is that possible? Unless you move the lead to outside (below)the boat to compensate for the less dense water. So perhaps that is the solution. Secure the lead to the bottom (outside) and not lay it inside.

[Thorne]

Sounds like a plan. Didn't some of the boats in the Gardner books show an external iron ballast shoe, sometimes even slotted for the centerboard to go through?

But I think most of this is moot. If the issue is the tow vehicle, I really think he'll never get the actual in-use weight of the boat below 1300lbs. And first-time builders routinely overbuild boats so that they weigh more than the plan...I know that I certainly have done this.

[TerryLL]

I'm with Thorne in thinking that's a lot of boat to squeeze into a thousand pounds. So maybe the question ought to be: "Why the 1000# limit?" Tow vehicle? Trailer? Garage floor? Other?

[Ignatius]

Hi Guys, I here what you are saying, but this not only about towing vehicle. I have various mountainous territory to cover in order to get to other beautiful (shallow ) waters, and I really would not like that kind of wear and tear on my 2 litre pick up truck. (used to towing 600 kg’s caravan, and would like to stay in that range, in other words, try to dercrease the weight of the boat by the weight of the trailer. If I aim for theretical 1000 lbs, maybe I’ll end up with as close to 500 + kg as possible. (But if compulsory, I’ll just have to tow all that lead)

I am on the forum to learn, and a carpenter by hobby ;-) so please correct the following logic, so that I can adapt to sound nautical advice. It is due to the fact that I am anticipating that the weight given by designers will be optimistic in terms of of lightest possible plywood, skillfull use of epoxy, etc, that I am trying to keep trailer weight down. The most important reason for the water ballast however, is versatility in enjoyment of the boat. Living near a beautiful river, and also a nice lake for sailing, I reasoned that one could just leave the unstayed mast at home (lug rig version-drop-in mast) and also dump some water ballast, and then do some river cruising.

1.I’ve studied the ‘controversial’ issue of water ballast via books, and on this forum, and it seems that it is well suited for specifically flat bottomed boats, having a tank from chine to chine below the floor boards (below the WL) An example her would be the Firecrest by Selway Fisher ( Sharpie/dory hull) (Got the plans for educational purposes only) Note: The ballast ratio in this case also being more or less 50/50 – 450 lbs hull/ 400lbs water ballast- as in the case of the both the NIS 18, and also the Thomasson sharpie: Hull 300 kg, ballast 290kg. (Same principle more less also for the NIS 18 too).

As someone said: The ballast is roughly the equivalent of hiding 3 people beneath the floor boards where they will stay, amongst other things , to help self right the boat. OK, so I want to get rid of two of these people, cause they do not pay for gas. The one person remaining I will allow cause he will be used to trim the boat.

2. My reasoning is that if ballast is stipulated to be from chine to chine below floor boards, (and below WL of course,) as is the case in both the mentioned Firecrest and the Thomasson sharpie, then it doesn’t matter weather rocks, lead, water, sand, concrete, OR A COMBINATION of these materials are used. Please note that the Thomasson sharpie is self righting with the specified internal ballast only. Also compare various Reuel Parker sharpie designs. Quote from Terrapin 21’ design : (internal only, as I understand?)




BALLAST

800 lbs. total, internal + water, fuel and stores to trim OR 400 lbs. lead, 400 lbs. water ballast; remainder in stores


So, if this ( the combination of water and lead) can be done on various other sharpies,(like those of Reuel Parker) why not also the NIS 18 or that of the Thomasson design? – With the blessing of the designers, of course. (Will never dream to tamper in a reckless way)

3. Excuse the long posting, but my question still remain: How to install the combination of lead and water; thin lead sheet with water tank on top? Next to each other, etc? Just wondering if anybody practically familiar with the Reuel Sharpies could share something. But I think I’ll just contact my very helpful designer on the ‘how to’ of this one…as I said, we already agreed on the principle. It all boils down to the fact that although this particular design was not designed for water ballast, the Sharpie hull, as a type, can be considered friendly towards such an addition. But as said, any amateur must please be corrected…..regards to all.

[Tom Robb]

Free advice is worth what you paid for it.
Contract (pay) with the designer to work out your scheme, or pick a boat that actually fits your requirements.
We all want what we can't have. The secret of contentedness is to be happy with what you can have.

[Ignatius]

The matter of water ballast plus lead was settled months ago with the designer. Just wondered about the spesific configuration, but it is sorted out now. And whatever the resulting trailer weight of the boat may be in the end, the compromise of lead+water ballast is satisfactory to me. Thanks for all the well meant advice. To each his own. Greetings.

[TerryLL]

Glad you got things worked out. Send pics along when you get the build under way. I'm real curious to see how the water tanks fit in.
Best, Terry.

[JimD]

Ignatius, if the original plans call for laying lead inside then my response
Secure the lead to the bottom (outside) and not lay it inside. is still the only way to keep the CG from moving up if you convert some of that lead to water. Good luck and hope you keep posting as you build. Its a really nice looking sharpie.

[Bill Mercer]

Ignatius, I think the concerns people have is that water ballast will raise the cg of the boat--if it's ballasted with lead sheets on the inside of the bottom, the vertical center of the ballast tanks will be higher than the vertical center of the lead would be, negatively impacting ultimate stability and self righting (if the design was self-righting to start with). When the designer says, "Sure, go ahead and do it, if the cg doesn't move," that's probably an impossible condition. Now this may not be a problem for you, depending on the conditions where you will be sailing. Also, if the water ballast ends up further forward than the lead would be (i.e., under the v-berth), the boat will be down by the head, which is dangerous with sharpies. The heel of the stem generally needs to be out of the water to prevent scary steering going downwind in waves (so sayeth the awesome and powerful Chapelle, not to mention Phil Bolger). You can move the lead back to compensate, but you might want to do some calculations first, and then having more weight in the ends might increase or deepen pitching in some conditions.

Speaking of Bolger, his Micro is selfrighting, and the bare boat with ballast weighs around 1000 lbs., I believe. He uses a shallow, hollow keel with 420 lbs of lead, plus water.

[Ignatius]

Hi Bill, bit of a late reply this, sorry. Appreciate what you say...raising the CG is a real concern.

For interest sake: The Thomasson sharpie, as designed, has two internal lead sheets, both accross the full width of the beam: both one inch (3cm)thick and respectively 1'6" wide (440 lb, under aft part of the V berth) and 6" wide (160 lb, just aft of the cabin, under cockpit floor) So it seems that, provided one uses this ballast area only - with the correct total weight and correct ratio of water-lead, the CG will not change, if I understand correctly?

The compromise it seems , will be a less lively boat, a more complex build, and sacrificing storage space. Headroom will stay intact. However, the influence of partial water-ballst on aspects like CG, self righting ability, etc, seems to be too controversial, and too delicate for this newbie to build this design with the confidence it deserves. In a boat with only 10"draft, and presumably therefore the very high ballast ratio, one would not like to take chances tampering with ballast, even though the designer gave a thumbs up. But oh, the temptation, the temptation...

Thanks to all.

[johngsandusky]

I think that changing the center of gravity is important if the change is significant. We all agree that dense ballast, low in the boat is best. But I think if you work out the centers of ballast weight for a flat bottom boat with inside ballast, you'll find very little variation caused by density. That is to say that if the lead were one quarter inch thick, and the water ballast is three inches deep, than you're only changing the center of gravity of the ballast by an inch and a half, which will change the center of gravity of the boat by less than an inch. Inside ballast in flat bottom boats is least sensitive to changes in density because of it's short lever arm.
He'll be fine. And if the boat turns out to be too tender, he can always add ballast later.

[donald branscom]

I have the perfect solution.

After you build the boat. Take a 4x4 and cut it in half and route a grouve in each side,
Then glue it and screw it into the boat 10% aft of center.

Next slide the axle thru the hole and the bolt on the wheels.

No trailer neeeded.

OR...
Bolt a plate on the transom with a large 2 road worthy castor wheels and then bolt a trailer hitch on the front.

No trailer needed!

The trailer IS THE BOAT. ONLY one registration needed. Boat or trailer take your choice.

[Ignatius]

Donald, sorry your'e late, someone's already done that:D ...Quote from http://www.atkinboatplans.com/retreat :

"Fact is it would be no trick at all to fix a pair of automobile wheels each side at the middle point of the over-all length, making a trailer that at the same time would be a house boat. Axle would not be required, nor springs. Two front knuckles from a heavy car welded to suitable plates could be through bolted to the sides; then removed after the trailer had been wheeled down into the water. With approved hitch to attach to rear of automobile, and driving at modest speed the whole would function very well. This is worth thinking about. The total weight of the boat without personal items will be approximately 1,900 pounds."

So please don't get any 'patent pending' ideas...

Johngsandusky, Sir, you are the man. That is exactly how I understood the water-lead combination....and having 50 % disposable ballast will really help me in the quest to try and keep total towing weight down to less than 1500 lb....

So maybe I'll just file the ballast issue as 'still not totally ruled out'...:o

Cheers.
(PS pardon grammatical mistakes, not English speaking)

[Woxbox]

I think you're on the right track considering what you want to accomplish. Personally, I would just buy a bigger truck, but if that's not an option, then move ahead.

It sounds to me like this boat will spend its time in well protected waters where you just won't encounter any big seas. If that's the case, then raising the center of gravity 2" or even 3" should not be cause for worry. Keeping the cabin structure and rig as light as possible will also help all around, of course.

When boats of this type and size are built to be self-righting, they have very significant stability in flat water. I think you'd have a hard time capsizing it even if you tried.

[Ignatius]

Good to be assured in this way, Woxbox. You guys have been very helpful. May I just quickly mention that the issue with the water ballast is not only about the towing vehicle (by the time the boat will be launched, my present wheels will be rusting in some scrap yard anyway!) Lots of other advantages also, mainly linked to own style of intended use.

It is also about single handling (launching and retrieving) And I need the boat to float quickly off the trailer, preventing the rear axle of the vehicle to be submerged. (depending on the tide)
In one or two places I'll again need a very shallow draft, even less than designed, to get over shallow sand banks (much less than a feet at low tide) in order to get to desired waters.Therefore every inch helps. Will take in the waterballast once in those open waters. (well , that was the initial line of thought anyway) I hoped it would help preventing the long wait for high tide in order to launch, and therefore increase sailing time, :) etc. Hope this makes sense...

Comment: Never expected any established forum members would defy the holy laws of boat building, and commit the ultimate sin of telling some new guy that it is actually OK to raise the CG of a boat...:D

Thanks again.