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Boat Design And Bridges.

Ray

By Ray
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Ray

Ray

Posted
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Inspired by MM's thread but not wanting to hijack it, there was a suggestion for a submarine to deal with that bridge. Later there was talk of extra ballast.

Is it a pure flight of fancy to think these two idea could be combined, surely it would not be technically difficult to have floodable tanks incorporated with decent pumps dedicated to them.

Approach bridge, flood tanks, pass under bridge, empty tanks. No extra draught for shallow areas after the crossing.

No doubt a bit of clever engineering will be needed in the design, location and capacity of the tanks to ensure an even keel, but that's not difficult for those with the knowledge and skill.

Could even be added to pre-existing boats with a bit of care.

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MauriceMynah

MauriceMynah

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It sounds good Ray, but sadly it's a non starter. The water inside the boat weighs the same as the water outside the boat. I know that's stating the obvious but the effect of it may be less so. 

For every inch lowered the volume of water required is equal to the area of the vessel times 1 inch. so, roughly speaking to lower a 30' craft by one inch requires 26.25 gallons of water. To reduce the airdraft from 6' 6" to 6' requires tanks to hold 137 gallons. Rounding things down a bit, think of it as 3 x 40 gallon oil drums concealed evenly in a 30 ft boat

So this is, in essence, is the problem. To make any significant lowering, the holding tanks would have to be many and evenly spread. Not easy . 

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expilot

expilot

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Against my better judgement, (the hire yard owners insisted it was done) I have taken a boat through Potter bridge with flooded bilges.  A truly terrifying experience.  Without baffled tanks, the water slops for and aft inside the boat and from side to side.  I would have felt happier sitting astride a 35' blancmange.

 

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MauriceMynah

MauriceMynah

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3 minutes ago, expilot said:

Against my better judgement, (the hire yard owners insisted it was done) I have taken a boat through Potter bridge with flooded bilges.  A truly terrifying experience.  Without baffled tanks, the water slops for and aft inside the boat and from side to side.  I would have felt happier sitting astride a 35' blancmange.

 

I think I might have been tempted to suggest that the hire yard came and did it themselves!

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Ray

Ray

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7 minutes ago, MauriceMynah said:

Galileo, what a star eh.

I think it might have been Archimedes who was interested in the problem, but I'm not sure where he kept his boat.

I do tend to get my geniuses mixed up! ☺

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BrundallNavy

BrundallNavy

Posted
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6 hours ago, JanetAnne said:

Us woodies just turn the bilge pump off for a few mins. :default_hiding:

I did but it was taking an age :default_hiding:

Plan B. Take out the weed filter and turn on the valve, make a cup of tea then turn it off reinstall the filter and then find your now on the bottom.  :default_dunce:

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SPEEDTRIPLE

SPEEDTRIPLE

Posted
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7 minutes ago, brundallNavy said:

I did but it was taking an age :default_hiding:

Plan B. Take out the weed filter and turn on the valve, make a cup of tea then turn it off reinstall the filter and then find your now on the bottom.  :default_dunce:

Put some wheels on the keel then :default_laugh:

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SPEEDTRIPLE

SPEEDTRIPLE

Posted
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4 hours ago, ChrisB said:

Quite a few trailer sailers have water ballast, Macgregor, and Swallow boats for instance.

I believe McGregor made a 26ft power sailer, which was light to trail, with the 2 piece mast down on deck and a big outboard over the transom was a speedboat, then raise the outboard, drop the centre board, pump water into the ballast tanks, hoist the mast and sails, and sail away?. Was that the one?.

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ChrisB

ChrisB

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10 minutes ago, SPEEDTRIPLE said:

I believe McGregor made a 26ft power sailer, which was light to trail, with the 2 piece mast down on deck and a big outboard over the transom was a speedboat, then raise the outboard, drop the centre board, pump water into the ballast tanks, hoist the mast and sails, and sail away?. Was that the one?.

Yes, but they dropped the two piece mast. There are a few on The Broads. However I have been told because Broads water is fresh and non too clean it can go stagnant in the tanks and the smell begins to make the boat smell like a pond. I was interested in a Swallow Baycruiser 23 and was in talks with them about ballasting using a hosepipe with a cup of bleach added for good measure. The best power sailed along the lines of the Macgregor was the Odin 28 but they seem to only be available in Canada now. It was a much better built boat.

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SPEEDTRIPLE

SPEEDTRIPLE

Posted
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1 minute ago, ChrisB said:

Yes, but they dropped the two piece mast. There are a few on The Broads. However I have been told because Broads water is fresh and non too clean it can go stagnant in the tanks and the smell begins to make the boat smell like a pond. I was interested in a Swallow Baycruiser 23 and was in talks with them about ballasting using a hosepipe with a cup of bleach added for good measure.

Yeah, i had`nt thought of that. As for the bleach, the problem would be, where to drain the tanks if on the water?. To pump it outboard would surely be against regulations?. Or is it in the tank permanently until you lift the boat out?.

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CambridgeCabby

CambridgeCabby

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No need for water ballast , moor up this side of the bridge , go to the pub , have a few pints (just to be sociable, of course) , grab a dozen or so patrons  get them aboard go through the bridge moor up , back in the pub (few more pints to be sociable of course) and Bobs your uncle 

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ChrisB

ChrisB

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23 minutes ago, SPEEDTRIPLE said:

Yeah, i had`nt thought of that. As for the bleach, the problem would be, where to drain the tanks if on the water?. To pump it outboard would surely be against regulations?. Or is it in the tank permanently until you lift the boat out?.

Different methods for different boats. The Macgregor has no pumpout, you either do it on recovery or open the valves and take her up on the plane! Not a Broads option. The Swallow has a pump. I don't think a cup of bleach would be bad. Our water here comes from a Tower and is highly chlorinated, from the tap it stinks of bleach. I filter it before I make tea.

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grendel

grendel

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I think i have the solution for maurice mynah, fill the ballast tanks with beer, that will get you under the bridges, and then connect them to a bar pump for emptying purposes, you just have to remember to top up the beer in the ballast tanks when you need to go under the bridges.

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SPEEDTRIPLE

SPEEDTRIPLE

Posted
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37 minutes ago, grendel said:

I think i have the solution for maurice mynah, fill the ballast tanks with beer, that will get you under the bridges, and then connect them to a bar pump for emptying purposes, you just have to remember to top up the beer in the ballast tanks when you need to go under the bridges.

And probably drink it ALL in celebration when he gets to the other side :default_laugh:

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