SB18 bulb weight

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giuliano68
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SB18 bulb weight

Post by giuliano68 » Wed Sep 23, 2015 3:13 pm

Hi, I did the model of sb18 bulb, but according with my calculation
the weight is not 163 kg. (360 lbs) but only 148 kg. about, because of the hole to put the keel
Could you confirm my calculation?
In this case how can I do? It's necessary to increase the lenght of the bulb?



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jacquesmm
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Re: SB18 bulb weight

Post by jacquesmm » Wed Sep 23, 2015 3:47 pm

Lead density is higher in the US . . . :lol:
We probably did not calculate the volume of the hole but it is not really a large hole, it is just a steel bar 2x2 " (5 x 5 cm), not the whole profile. The weight of the hole is probably 1 or 2 kg minus the weight of the steel bar that fills it maybe 500 gr?
The difference is irrelevant that is why the plans say "about" 360 lbs.

We can not calculate the weight of the boat or the ballast ratio with that much precision.
Because everybody applies fiberglass a little bit differently, your hull weight itself will vary by tens of kilos. Plus the weight of accessories, hardware, gear.
I would not worry.
Jacques Mertens - Designer
http://bateau.com

giuliano68
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Re: SB18 bulb weight

Post by giuliano68 » Thu Sep 24, 2015 5:24 pm

In the project, plan #D281/4, I can see that the volume of the hole is bigger than 5x5 cm., it is 37 cm length, about 4 cm. width (with foil section) and 12 cm. height, and I can't find any 5x5 cm. steel bar.
Do I have the correct plan?
If so, the volume of the hole is about 15 kg.

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jacquesmm
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Re: SB18 bulb weight

Post by jacquesmm » Thu Sep 24, 2015 6:48 pm

The profile does not extend through the bulb, only the steel bars.
I"ll post a picture of the plans tomorrow showing where we mention the steel bar.
Anyway, if that 15 kg is a problem, enlarge the bulb by 4% and it will be 15 kg heavier.
Jacques Mertens - Designer
http://bateau.com

giuliano68
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Re: SB18 bulb weight

Post by giuliano68 » Sun Sep 27, 2015 2:16 pm

"I"ll post a picture of the plans tomorrow showing where we mention the steel bar."

I'm sorry, but I can't find the picture of the plans you posted, could you tell me where I can find it?
Thanks.

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Re: SB18 bulb weight

Post by jacquesmm » Mon Sep 28, 2015 9:23 am

Sorry, I was looking at a drawing for another keel, not the SB18.
The SB18 keel is built as shown on your plans, around a wood beam, not a steel pipe.
And it is true that this makes the hole bigger than what it would be with a steel pipe.
I ran the calculations again and for the volume of the bulb without the hole, the weight should be 172 kg.
The plans say 163, that means we must have subtracted the hole for the profile core, the wood beam.
Maybe you removed the whole profile with the glass and we calculated only for the rectangular beam?
Our model shows the bulb volume to be 930 cubic inches = 15.2 liters.

However, 15 kg difference is not relevant.
Look at the CB option, there is 114 kg difference that we compensate for with lead ingots on the bottom.

And if you want more weight in the bulb, scale bulb by 2.2 instead of 2.
(The plans show a 2:1 bulb template that you must scale anyway)
Jacques Mertens - Designer
http://bateau.com

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