# Houseboat weight

Discussion in 'Boatbuilding' started by boulty123, Mar 2, 2013.

1. Joined: Mar 2013
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### boulty123Junior Member

I am planning to build a houseboat using polyethylene pipe for the pontoons.

There is a local company who specialise in cutting and welding large diameter pipe for this purpose.

My problem is how to calculate the size of the pipe I need for the weight of the boat.

If I am understanding the principles involved I need to find the volume of the pipe in cubic centimetres (Pi x R x R x length), divide by two (to allow for half submersion), divide by 1000, and that will give me the displacement weight in tonnes. The fluid medium will be salt water.

Have I got that right??

2. Joined: Aug 2007
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### CDKretired engineer

Yes that's correct.
Have you thought about the effects of temperature like expansion, contraction? Half immersed long tubes will not stay straight if the air and water temperatures are different.

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### boulty123Junior Member

I have not thought about that. I know that polymer hulls of various types are fairly common in Australia, and I have not seen that discussed before.

The pipes used are HDPE rigid I believe, and very thick. They are also in common use for above ground drainage and reticulation applications, which I imagine would simulate those same conditions.

I will put that to the supplier. They must have had some negative experience if that is an issue. Perhaps venting may be a necessity.

4. ### Submarine TomPrevious Member

You will want to increase your freeboard on those pontoons.

50% is not enough.

Otherwise 33% is a safe option.

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### MaVNew Member

If you divide cubic centimetres by 1000 you get liters or kg, if you want metric ton divide by 1000000 or just use meter not cm.

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### boulty123Junior Member

Of course, thanks MaV. Not thinking - seeing kg and mentally converting to tonnes.

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### boulty123Junior Member

Good point Tom. I was looking at what would be the maximum displacement for safe floatation. In my calculations of permissable load, I was factoring in no more than 70% of safety maximum, which is 35% of total pontoon volume.

Thanks.

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### PARYacht Designer/Builder

One of the first tasks you perform after a GA, is a weight study. Some quick calculations about what weighs what and where they will live on the boat. This will give you a ball park of what you need to support (and where), so adjustments to your hull(s) can be made.

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### Manie BSenior Member

Whoa
stop right there

THIS IS A LOUSY IDEA

The hulls are 10% (or Less) of the cost of a houseboat

boulty123 please do yourself a favour
BUY A SET OF PLANS from a well known source

10. Joined: Nov 2003
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### PARYacht Designer/Builder

What buzz kill Manie. Let him do a center of masses calculation manually and learn for himself how much fun this stuff truly is.

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### Manie BSenior Member

I hope I did not rain on his parade - If someone wants to build a boat - go for it by all means.

During my years at Xstrata chrome mines in Rustenburg we laid kilometers of HDPE pipe. We were pumping very abrasive slurry. Murphy's law dictates that when a big burst occurs it is often in the middle of the Night / Weekend and the loss of production meant that all senior personel had to be on site.
Got the Tshirt!

PE or HDPE pipe is heavy and is designed around certain working pressures and abrasive requirements.
Definately NOT boat building material.

when I look at the/his first question I worry
ouch

12. Joined: Sep 2006
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### Manie BSenior Member

boulty123 make a drawing and post it
hand drawn and scanned is perfectly ok - we will get your general idea.
Then the guys can give you plenty ideas and info.

Top Tip
the drawing is of your boat - just the boat as you see it

13. ### Submarine TomPrevious Member

Of course you are all correct but if he doesn't ask if it's a good idea or not... what are we to do?

I was just trying to entertain the enthusiasm.

It is a terrible idea but, as PAR says, it's a starting point.

These things rarely ever get built anyway.

Carry on boulty123, as you were.

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### FMSSenior Member

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### ScottymJunior Member

Hi, I have done this and can tell you its the best material for a houseboat.I used 1000mm diam pipe - 30mm wall thickness. I welded in baffles so I have massive tank storage for water and all waste water.
I can tell you there are no issues with expansion re the comment about water and air temp - the water soaks any heat buildup. On land a 12 meter pipe will curve about 150 mm out of line on a 35 degree day. (bends one way facing the morning sun and then as the sun went over head and down in the west it curved back the other way and then cooled to be straight again at dusk!)
Beauty of this stuff for a houseboat is this:
1. weight is not an issue for a houseboat and easily compensated for by extra pontoon if required - depends on your overall size.
2. No rot, no corrosion
3. No worries about "parking" it on rocks or rough ground.
4. Marine growth easy to get of with no damage to hulls either - you can paint and antifoul it succesfuuly as I have done.
5. Its an easy material to work with ,cut or weld.
Flotation is easy to work out - pick a depth of floatation ( I use 40% of tube diam) - use the ABE calculator on the net for volume of a lying down cylinder - this gives you the M3 displacement and this is your load capacity. Remember to add the weight of your pontoons to the mass you want to float. My 38 ft ended up at about 9.5 T and draws 400mm. I recommmend 600mm freeboard on enclosed river like the hawkesbury river - the big powerboats can setup a swell that will cause problems ( most houseboats I have talked to with less than this have had water onboard).
Mine is trple pontoon and in 5 years the champagne flutes haven't ever toppled over - in hurrican and worst river conditions and swells from passing hispeed palaces!

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