Reducing boat height by 5cm (two inches) by ballast

[healhustler]

Skyhawk may have half a good idea. Just stack kegs of beer for the huge group of guests you’re potentially going to invite, and use the beer instead! Have a party after you clear the last bridge.

 

[skyhawk]

keg's...as in multiple?
probably more laughs to be had that way!
I was picturing more like 6 or 10 folks standing up on the bow to see if you get a measurable displacement....even if only 1/4 inch...
but just using kegs as a ballast.....good idea!

 

[Buiz]

I think the suggestion to add people was only as a trial
to see how much a measured weight on the bow will push it down....
then with that information you can better extrapolate how much weight you might need in terms of water weight, etc... for the actual trimming.

drop a plumb bob off the bow to the waterline. Then invite several folks from the marina willing to tell you how much they weigh (so men, not ladies) over to stand on the bow...

it could be a drinking game....maybe buy some beer as bait to get them to come over....
the game...how many 200 pound men does it take for the desired change in height.....
make a video and post on youtube....maybe worth a few laughs

That's genius. Apart from the various drinking games that this exercise will obviously lend itself to, I'm arriving at the following concept thanks to your great input: in completely calm water I'll paint a clearly visible mark 12cm above the present water line on the bow. I'll then invite marina folks (gents only, of course) onboard on the front deck successively and noting their weights until the bow is 12 cm down. That will give me the weight needed in addition to, I'm sure, a few laughs, rude jokes and glasses of red wine.

I'll then proceed to organize such weights in water barrels. Done!

 

[skyhawk]

just count me for an assist...it was Old Dan 1943's post. I just turned it into a party

even if you only have enough folks to drop it a fraction of your target, you'll be able to get close....
I thought the title was 5cm.
regardless...whatever your target
put your mark under/abeam with your boat's high point, then get the people to stand approximately where you'd put the ballast. Even if you only have enough folks to drop it a fraction of your target that should get you close enough....ie if your test only gets you down 25% of your target, then multiply the total weigh of people x 4. That'll be a little low depending on hull shape, but it would be a good starting target I think

 

[Giggitoni]

My GB42’s fresh water tanks are inside the laz on the transom. When the water tanks are empty by bow sinks about 3cm (stern rises). Full fuel tanks lower the whole boat about 2cm. Do you have an all-chain rode?

 

[lwarden]

I would be looking for a lot of used chain to weigh the boat down. In sections it's simple to spread out in the bilge and is fairly inexpensive.

 

[OldDan1943]

I'll lend you 250ft of chain, return it when you finished with it.

 

[rgano]

If I read correctly, this lowered air draft is intended to remain in place while navigating an extensive canal system. I would be skeptical of the boat's steering response after a significant weight addition at the bow. Might I suggest a quick call to Grand Banks to find the tons per inch immersion for the boat and plan to add the weight throughout the bilges. Do NOT put that much water in there as the free surface affect will have you sloshing from port to stbd list and in any seaway endangering the vessel. Adding a bunch of weight on deck is a bad idea too for structural reasons. One day I found about ten of so passengers had migrated to my GB42's flying bridge. The doors to the deck from the main cabin would not open.

 

[Benthic2]

This is a fairly complex problem. I think the first step is finding the pivot point for your boat. The easiest way to do this might be to have a video camera record your boat as you move a weight from the bow to the stern. Mount a camera directly abeam of your boat and have 4 guys walk from the bow to the stern and back a few times. Then with some video editing software you could find the exact position ( fore and aft )that does not move. Once you know that position, you'll have to determine it's relation to your highest point. Only then can you determine if you need to raise or lower the bow or stern. Instead of adding ballast you may find that the solution is to inflate an airbag under your swim platform.

Another option may be to plan around a rainy season. There must be seasonal variances in the water level. Figure out what they are and use them to your advantage.

How close are you to one of these bridges ? Have you physically visited it and verified the clearance ? If there is any conservatism in the stated clearance you may be fine as you are.

 

[skyhawk]

rgano makes some very good points I think....

but it also strikes me that the weight required to draft 2 inches might not be all that much...especially if not trying to draft down level

just spit ballin I'm feeling like 3,000 to 4,000 pounds is the ballpark to go down LEVEL
(based on 35ft x 10ft x 2 inches deep = roughly 60 cubic feet = 3,744 pounds)
but
if you just want to tip the boat (not level) to go under a bridge, could the water be pumped aboard before the bridge then drained off after the bridge is passed....

I saw a youtube video a while back...MV DIRONA I think was the name...where they placed some rather large fuel bladders on deck for a passage. That's what I'm picturing...but a much smaller scale.

regardless...great points about calling the builder!

 

[psneeld]

Place a stick on the dock with a measured mark on it you want to achieve.

Use a cheap laser level on the highest part of the boat pointing at the stick (I had a $15 one from a builders supply that cast a pretty wide horizontal level line.)

Have people get on the boat and walk to the bow. Note their weights and keep adding till you make the mark.

No need to over think or over engineer this. The final addition of weigh to the boat, no matter how you do it though should be though through the safety level though.

 

[OldDan1943]

\...great points about calling the builder!

 

[Benthic2]

If the pivot point is forward of the highest point, weight on the bow may RAISE the highest point.

 

[Peter B]

Thanks for all the input. As I told backinblue, tight clearance is par for the course on European canals. New boats that are built here with canal cruising in mind are built to standard spec of 3.45m height. I'm 3.55m and will ballast down by -10cm so I'll achieve the standard spec height.

It's 349 bridges over some distance so getting people onboard is not practical. I have removed the windshield, the compass (that otherwise would poke up) and even a railing or two. There's nothing more to remove unless if I take a saw to the polyester, which I've decided against.

That being the case, and possibly this has already been suggested, it sounds like you are close, and only need to dip the for'd end enough for comfy clearance. So as this modification is going to be needed for the time to complete the trip under all those bridges, but not to be permanent, it still needs to be done in a convenient, non-destructive way.

How about emptying the lazaret water tanks, and placing one large capacity turtle pack type bladder for your fresh water on the for'd cabin floor..? Connect it to the closest fresh water draw point, and have the filler opening easily accessed through the for'd hatch. (I used a triangular shaped one under our for'd cabin floor as our reserve freshwater. It actually improved the trim, because all our other tanks were in the lazaret.)

You'll then still have the saloon and aft cabin for accommodation and sleeping. You'll also have plenty of water, but also easy to top up as you go to maintain the droop snoot trim enough.
The fuel then could be used as per normal - less is more (droop), that is. You could still estimate the weight of water needed by the human trial/free beer trick to begin with. Then all that needs to be done at the end is reverse that process back to usual set-up.

 

[Chartwell]

Hi 2 years ago I moved my GB 36 classic from Portsmouth (uk) to Cannes via the French inland waterways. Very tricky at times and used various tactics to successfully complete the journey without any damage. First observation is that you cannot rely on the 3.5 metre minimum bridge heights. Lots of variables. Very happy to assist if you can get in touch with me. Regards Fred

 

[sicconim]

Hi,
we also went from barcelona to rotterdam through Rhone, Saone, Rhine. We cut the flybridge reling and added 800 liters of water in the spanish mineral water 5L bottles that are otherwise thrown away. With the water, we won 3cm on a 15m boat weighing 37tons! We still had 3,53m height, but it worked because water level was low. Good luck!
Marco

 

[Circumnavigator]

I'm with BandB -- you're figuring this far too close. My impression is that the French canals can vary with season and recent rain by far more than a few inches. I wouldn't try to go under bridges unless I had at least six inches and a foot would be better. The only thing in your favor is that isn't a sailboat where you can't see the lineup -- you'll be able to eyeball every bridge.



I also think your calculations come out too high. Fintry (79', 320,000 pounds displacement) runs 6,500 pounds per inch. If we assume that the GB 36 is about the same shape -- close enough for estimates anyway -- she's 45% the length, so has 20% of the water plane area and would take 1,300 pounds to sink her an inch -- about 5000 pounds or 2300 kg for your 4 inches. Admittedly, this is a very rough calculation, but it shouldn't come up with a factor of two difference.


Jim

 

[steve marcus]

Ballast

I would think you do not need as much weight as you have calculated. The bow is the narrowest part of your boat and as such does not offer a great deal of flotation. I became aware of this because I added 70 metres of 3/8 anchor chain off my old boat to the 100 metres that were already on my newly purchased boat think you can't haave enough chain and it affected the trim drastically and I had to remove the chain or put some ballast in the lazarette (it already had some lead ingots in there)
I seemed to me that the boat almost pivots on the centre point where she is also beamiest. My recommendation would be to borrow some chain and feed it into your anchor locker and see what happens, it will cost you nothing but a bit of work and may fix the problem

 

[Chuck in WA]

Not nearly as much fun as a keg party, but water ballast bags used in wakeboard boats could be an option.

 

[gilbertpark]

I went through a similar thought process when contemplating bringing a mainship 35 through the canals. First point is that you will increase the draught of your boat. You don't say what it is, but increasing it may cause grounding problems.

Second point is be careful where you put all the weight. A surveyor friend of mine warned me that you could potentially make the boat unstable with weight high up (on deck or even higher). While there are no big waves in canals there can be huge amounts of wash from some of the big commercial boats travelling fast in the big river sections. This and the extra ballast might be enough to capsize the boat.

Thirdly another friend suggested having a few crates of inexpensive wines, a few baguettes and a load of cheese. When you come to a low bridge (only a few are at 3.5m) invite all the people watching on board for a bridge party. Put them all over the boat to keep weight low and once you are through ask them all to leave, unless they want a long walk back!

two suggestions are serious one is tongue in cheek!

Gilbert

 

[Richard Hoffman]

I am going to need to do above on my Grand Banks 36. The boat is the highest at the front of the flybridge, so I need to weigh down the bow by 5-7cm. I guestimate that I will need a ballast of 2000kg or so to be placed as far forward as possible on the boat. My best idea so far is to buy barrels and bladder tanks and fill them with water. Sand or cement will have higher density and thus take less space but it'll be cumbersome to get the material and discard it again when I've passed the area with low bridges that I need to pass. Anyone has any experience with this kind of ballast and any tips and tricks?

Use Lead weight, most weigh per area

 

[NeuroBeaker]

I'm with BandB, tungsten is the cleanest, easiest, most expensive way to weigh the boat down. You could always sell the tungsten cubes when your done. Getting them in and out would be a chore. But you might get lucky and make money on the cubes, they are getting popular.

Is there any danger of being mistaken for a tungsten smuggler?

All the best,
Andrew.

 

[Mobcat]

I had to put 5tonne of ballast in my trawler to put a second storey and flybridge on , I collected old anchor chain from the scrap metal bins at boat yards for a while it’s was easy to place deep in the bilge with PVC pipe as the conduit and is nice and flexible to get into those tight spaces, and of course I can move it around if my weight and balance changes due to upgrades mods etc

 

[cbouch]

I know that what I am going to describe does not apply to this particular problem because he is dealing in the metric system and we here in the u.s. do not. So, just want to call your attention to the advertised heights of bridges on the western Erie Canal. This summer we passed thru it and read warnings ranging from 15 feet to 15 feet 6 inches. Nys actually says the lowest bridge is actually 15.6 feet which is actually 15 feet 7.2 inches ...point being understand what the measurements really are telling you. Now, to the point of the question we were @ 15feet 6 inches after measuring many times using multiple methods. We ended up emptying our stern water tanks and loading the bow with our summers worth of ships stores...cruised the western Erie with room to spare.

 

[SteveK]

I went through a similar thought process when contemplating bringing a mainship 35 through the canals. First point is that you will increase the draught of your boat. You don't say what it is, but increasing it may cause grounding problems.

Second point is be careful where you put all the weight. A surveyor friend of mine warned me that you could potentially make the boat unstable with weight high up (on deck or even higher). While there are no big waves in canals there can be huge amounts of wash from some of the big commercial boats travelling fast in the big river sections. This and the extra ballast might be enough to capsize the boat.

Thirdly another friend suggested having a few crates of inexpensive wines, a few baguettes and a load of cheese. When you come to a low bridge (only a few are at 3.5m) invite all the people watching on board for a bridge party. Put them all over the boat to keep weight low and once you are through ask them all to leave, unless they want a long walk back!

two suggestions are serious one is tongue in cheek!

Gilbert

Obviously your first point is tongue in cheek as everyone know a GB36 is less than 4 feet draught

 

[BruceK]

 

[Mobcat]

I also meant to add just load up your chain locker with a heap of chain till it gets you nose down to spec, pretty simple and easy to remove and install with the winch ???? every ones a winner ??

 

[Xlantic]

It is possible to remove and re-attach the fly-bridge on the fibreglass Grand Banks, although maybe not so convenient for your trip.

If you plan to use the canals regularly, you might consider permanently removing the fly bridge.

 

[Xlantic]

You could attach a large container to the end of your anchor chain, drop it the water so it fills and then raise it until it is just off the water.

Since this places the weight very far forward it provides leverage to lower the bow with less weight.

But don't exceed your windlass rating!

 

[Xlantic]

MV/Rumbalotte, a Grand banks 36, has criss-crossed the European canal and river systems and written about it here (sorry, it is in German but the OP may understand):

https://www.rumbalotte.net