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Old 22 May 2012, 22:53   #1
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flex in SIB longside, front triangle

Hi,

I am new to this forum and to inflatable boats. I read loads of threats during the last weeks and got a lot of information.

Finally I decided to order a 3.3m SIB and a 30hp engine.

Now what I am considering is to bolt bars onto the alu SIB floor to make the boat stronger in length direction, considering the engine power.

Good idea or not a good idea? Does a SIB need flex in the long direction? I suppose at least for the alu boards in the middle it should be good. How about the front triangle? Does this have to flex (how much max)? If the front triangle does not flex there might be more load on the tubes, right?

Basically I wanted a RIB, but a trailer transport and storage are not an option at this point
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Old 22 May 2012, 23:25   #2
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Do you have a pressure gauge? If not you need to go and buy one. Most problems related to boat handling are pressure related.

Also if you are inflating every time a nice electric Bravo pump is going to be in order.

What horsepower is the boats max recommendation?
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Old 23 May 2012, 02:21   #3
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Well, the 30hp should be just on the limit. I am not really afraid it might fall off.

No handling issues so far, did not even assemble the boat, since i am waiting for the engine.

I am just a tech and like to pimp my stuff

So second part of the story is i want to fit some seats and a console. Question is do i have to fix the seat on one panel and the console on another panel, to allow the panels to bend slightly? Or can i put the items always between two panels with the bars to fix the panels solidly together, so the whole floor is like the stiff floor of a RIB?

So, the mechanical stuff aside, does a SIB have to flex (as a whole or just the triangle)? Or is it fine to reinforce everything? I want to modify if there is no argument against it.
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Old 23 May 2012, 06:04   #4
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3.3m and 30hp sounds like a threat to me....
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Old 23 May 2012, 07:07   #5
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I am aware that 30 hp are a lot for the boat. I take the safeties serious and will not crank it up right away of cause. Will drive it on a quiet lake

So basically that's what I am asking: if you are sitting in that boat, what is the threat? Which failure points have to be considered.

I will load the boat symmetrically and spread the weight over the length (forward controls).

Obviously the transom is a concern. I will bolt this with angles to the last aluminum plate.

Other failure points I see are the connections between the other floor plates. So i want to install the bars. Here I am not sure if there might be negative effects I am not aware of, so I started this thread.

Third: the tubes could be ripped off when breaking a wave. In my case on a lake it will not happen. But I would still like to have this covered. Maybe glue a second layer of PVC to where the tubes attach to the floor.
How could I effectively add straps?

Other things to cover?
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Old 23 May 2012, 07:31   #6
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We all love tinkering and others might disagee but if you want a RIB buy a RIB, trying to turn a SIB into a 'franken-boat' RIB will not a RIB make and seems fraught with hassle and potential problems. Once you have added all the weight and parts you describe and that will make the SIB 'non-deflatable' how will you transport it? Regardless how will you handle a 30hp engine - presuming this is even a two stroke it's a hell of a lump to lift, transport and mount.

A 4m Searider sounds likes a much more suitable buy?
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Old 23 May 2012, 11:30   #7
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I understand your concern.

I got the engine mainly because I want to upgrade later. It is not that much of a problem to swap the boat, but if the engine is too small for the next bigger boat it seems costly. That being said i could imagine a 4m as an option, just thought I don't need that much boat at the moment. But as you say it it makes sense. Maybe I will later look at a 4m zapcat to have sth. different that makes use of the engine. And some day hopefully a RIB of cause.

Regarding the engine (2stroke) I can easily limit the throttle to less hp, and reduce torque with a higher pitch prop. then I have a 15hp with 20Kg ballast. I will start slowly, promised I am not hunting for speed records. I know this boat is not made for it.

My question is also not how to make this boat ready for high speed.

As I said I want to make myself a seat and a console. I would also do this with a 15hp engine. Now my question is just: is it better to put each on a separate floor panel without any influence on the rigidity of the boat. Or place them in a way that the panels are stiff together? Would this make the boat better (more stability, the tubes do not have to hold bending force) or make it worse (increased stress on the collar of the tubes).
Especially: does the front triangle have to flex?
I do not want to make a crazy boat beyond its limits

No worry about the mechanical stuff, i will have everything reasonably strong and modular and with my means transportable. Otherwise no point in doing this.
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Old 23 May 2012, 16:13   #8
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Over on YBW.com they are always overpowering Sibs and Ribs, but its done in a careful and considered way, well most of the time Having said that, 30hp on a 3.3 sounds a lot. Most 3.3's have max power of about 15hp, doubling it is going to make it interesting and I think your transom and the join between the transom and the tubes will be the weakest point.

In reply to your question, with a Sib, the stiffer the better.

I got hold of a 3.1m Zodiac with floorboards when I was a kid and fitted a 8hp Yamaha. At 1st the front triangle floor board used to bend upwards when running at full power and into waves, this had the effect of halving the speed. My Grandad, a retired aircraft engineer, fitted titanium rods along the length of the boat and it was transformed, faster in all conditions and it felt much more rigid.

I know this is a rib, and a bit smaller, and its 'only' got 30hp !

http://youtu.be/TA9khGGbQlc
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Old 23 May 2012, 17:57   #9
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thats just plain stupid
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Old 23 May 2012, 18:07   #10
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Quote:
Originally Posted by Festinghouse View Post
thats just plain stupid
I agree. Is this a wind up
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