Forum > General discussion (Large)

Weight distribution?


Eddy Matthews:
It seems to me that a lot of the basics seem to be getting overlooked here, we've already discussed displacement - Something that should really have been calculated and looked at BEFORE buying a hull, but nevermind...

Now we move on to weight distribution....

Lets assume you have a boat capable of carrying five people before being converted to a paddler.... You fit an engine, drive system, paddlewheels, sponson and paddleboxes - they weigh the equivalent of two people, not unrealistic I think?

Now your boat can carry three passengers (in theory).... BUT!

You have taken up all the central area of the boat with your newly installed engine/drive system etc.... So you only have the option of two people in the bow and one in the stern, or two people in the stern and one in the bow.... This would almost certainly make the boat dangerously bow or stern heavy, as you can longer distribute their weight evenly!

So in practice you find that your boat can now only carry two people safely, and not five as it could originally. A dramatic decrease!

When buying secondhand hull with a purchase price of $160 and being a complete novice at boatbuilding displacement didn't seem to be a big thing.

However I'm still at a stage I believe where weighing etc is still an option.

Yes weight distribution is a problem, however there are enough smaller boats such as Rusty down in Australia or Gnatty for me to think it will work. I also believe Grebe could benefit in sitting lower in the water.

We plan on moving one of Grebe's 'benches' forward slightly creating more centre room and there is a large area already in the centre of the boat.

I never expected Grebe to carry too many people. In fact just me is technically enough for what I want her for, two's nice three's a crowd. Four was ok normally but got a bit squishy so keeping her down to two is pretty good in my eyes.

I think the sacrifice is worth it for a paddler  :wink:

It's true though Eddy they do all have to be taken into account in the planning stages. Placement of engine and accesories are going to be vital to the boats success on the water.

These trial remind me of (was it Mick) the trials in the paddling pool. If we could get something big enough and hold enough water (I think the government would call it a catchment dam in these drought times) and then see how she floats and how placement effects her etc.

Of course there is always the dam to take into account.

I know there are alot of the steam launches this size so I don't really see why a paddler would be too significantly different.

Roderick Smith:
Eddy's post explains why I bought a ready-made vessel (at greater cost), with sufficient size that distribution isn't a problem.
Over the last few days I have read an interesting post somewhere about the design of the Storer 7 m riverboat.  It was to go into survey for commercial hire, and so had to stay upright with four or six assessors all leaning over the one gunwhale.  It did succeed.
Major train ferries have ballast tanks with rapid-action pumps to ensure sideways stability during the loading/unloading of heavy rail wagons.
Concorde (the supersonic aeroplane) pumped fuel between fore & aft and wing tanks to maintain stability.
If fore and aft stability really is affected by the diffence between two and three passengers, perhaps ballast tanks would be a solution?

At worst, James could place his beautiful hull above the fireplace (like skiers have a set of 1950s hickory skis), and buy a bigger hull.  However, the world of steam-launch websites has many examples of small and stylish vessels which have surmounted stability problems.

James has assured me that, on his local river, waves will not be a problem.  He is lucky to find enough water to float a boogie board in Hopkins River at Maroona.  On most Murray River boating, the water is so calm that loading stability isn't a major issue.  Crossing Lake Alexandrina is a different environment, and has to be tackled only under the most-favourable weather predictions.

Roderick B Smith
Rail News Victoria Editor

As Roderick mentioned about small steam launcehs, Here is a 'felix launch' website 13' to 15' has the boiler up the front and four people in the back. Looks safe enough too.

I was always lead to believe wheels made the boat more stable on the side...I don't know if this is only rumour though.

The only waves on the Murray come from tourists on the bank!  :wink:
NB: Not true on Lake Alexandrina I believe! That's the website, scroll down to the one with the blue canopy to see a fully loaded and stable boat.

I do realise these boats have a different shaped hull just in case anyone wanted to bring that up!

In regards to not calculating displacement before purchase...when life gives you lemons for a very good them and make a dam good lemonade after!

Just a further note: The Boat Gnatty, although driven by an electric motor works. She's 14" in length and I've seen photos with her carrying 3 people. Although it does loook a little cramped for my liking!

I only ever wanted the SJ to carry 2 people at the most anyway.
Really, I think that the weight distribution cant be decided until it is floating, and as Derek suggested, get 10-15 mates all with weight stickers and place them in the boat until it gets to the correct water line.
From then you know how much weight you can put in the boat. (I know that is only the displacement not distribution)
But from then cant you just put the paddles on (dead centre) take that weight off the total, then put the engine under that connected to the drive shaft via chains, then have me sitting up the front or back (havent decided where I am giong to sit yet) and the other person sitting up the other end. The rudder system would be equalled by the front structure of the boat. As there any problems with that one :) ? I am not sure!!!
As Roderick mentioned ballast tanks are always an option, or just placing weights throughout the boat to make it more stable.
My hull bulges at the sides, giving quite a bit of stability now, which should play to my advantage!!


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