# Round Steel Pipe Barge Free board Questions

Discussion in 'Boat Design' started by Nick Gear, Feb 15, 2020.

1. Joined: Feb 2020
Posts: 3
Likes: 0, Points: 1
Location: New Zealand

### Nick GearNew Member

I have the following design:

The pipes are 762 mm x 12.0 m long, the total weight of the structure (as shown) is 4.1 tonne, the total pipe volume (displacement) is 16.4 m3.

My question is relating to calculating free board (or draft) on the radial pipe shape? Im assuming this wont be linear in relation to total buoyancy (i.e.) putting stability to one side, as further weight is applied to the structure, the free board isn't simply weight to total reserve buoyancy ratio?
Would I be right in assuming that i'd need to be calculating the circular segment surface areas of the 762 mm DIA in say 100mm increments to relate back to the various weights im applying..

Help!

2. Joined: Oct 2007
Posts: 3,390
Likes: 1,361, Points: 113, Legacy Rep: 37

### bajansailorMarine Surveyor

Welcome to the Forum Nick.

The total pipe volume is 16.4 m3 ; in fresh water the displacement at half the pipe depth will be 8.2 tonnes.

Your calculated weight of the steel work is 4.1 tonnes. So she will be floating at a draft somewhere between D/4 (190.5 mm) and D/2 (381 mm).

If you draw a circle full size with a diameter of 762 mm, then you could mark on draft marks at a spacing of (say) 20 or 25 mm between the D/4 and D/2 drafts.
The waterline will be slightly wider at a depth of D/4 + 25 mm (compared to the width at D/4) - you could safely assume that the cross section between these two drafts is a trapezium.
And then calculate the increase of displacement for each additional increase in draft.

Blueknarr likes this.
3. Joined: Mar 2002
Posts: 1,793
Likes: 456, Points: 83, Legacy Rep: 158

### BarrySenior Member

bajansailor likes this.
4. Joined: Feb 2020
Posts: 3
Likes: 0, Points: 1
Location: New Zealand

### Nick GearNew Member

This is exactly what I was after, thanks Barry
Intended use is accommodation platform - not a houseboat, but to house two smaller structures, and small commercial tiki bar.

5. Joined: Aug 2017
Posts: 1,432
Likes: 402, Points: 83

### BlueknarrSenior Member

6. Joined: Mar 2002
Posts: 1,793
Likes: 456, Points: 83, Legacy Rep: 158

### BarrySenior Member

If you look further into the page,if you know the height of the segment, or partial circle, it works out the area

7. Joined: Feb 2020
Posts: 3
Likes: 0, Points: 1
Location: New Zealand

### Nick GearNew Member

Thanks Blueknarr.
We've got limited payload atop the structure, with a wave Hmax <400mm sitting in a sheltered Fjord within a marina.
Total displacement of structure would be no more than 6.8 - 7.0t including payload.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.