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Old 01 March 2005, 16:42   #21
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What a response !
I will be talking to Henrik at Ullmans tomorrow. Shall give him a link to this thread, maybe he will have some comments to your theories Tim.

Hopefully the boat will be delivered in Norway first of April.
Will post a report after some serious testing.

Regarding the holes in the springsystem, guess I have to throw away my Bermudashorts and go for tight underware : )

Regards
Roy
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Old 01 March 2005, 16:43   #22
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If money were no object then a set of seats that would stop the bonecrunchingheadwobblingarseachingteethcrunchingn eckcracking 'whoops I timed that one wrong', and if these seats are the ones to stop it...excellent I will have some.
They look the mutts anyway so why not.
No worse than having an 'a' frame to hang a couple of lights on is it?
I want 2 of them but they would double the weight of my boat!! arf
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Old 01 March 2005, 16:43   #23
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Ah, Slimtim I see what you are getting at. You mean the direction you feel the hull would move is not directly inline with the centre of the spring/damper? If so, it does not matter because the seat fulcrum will move upwards in that direction since it is directly connected to the hull, thus the spring will compress.
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Old 01 March 2005, 16:50   #24
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To move on a bit, I'm surprised at the lack of rib seating which has good lumbar support. Essential to keep that lordosis ya know.
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Old 01 March 2005, 16:58   #25
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Richard, it probably would've been if I had thought of it! Instead I'm investigating manufacturing techniques for advanced composite wings...still quite interesting though.

Jeff, Good point about the wheel barrow. However the bit about the movement not being in line with the shock centre line is not what I'm on about...sorry! The forks are just an example. Mountain bike designers generally try and get the rear wheel to match the path of the front, but this obviously doesn't require the wheel axle movement to be in the same line as the shock stroke. Clever linkages and Virtual Pivot Point designs (I won't get into that!) help to acheive this.

I'm trying to think of a better way to explain myself. Perhaps imagine the force from a wave being "transmitted" into the hull and then up that linkage straight into the helmsman's arse. If the linkage was the other way, this force would cause the hull to move upwards more freely and the energy would be converted to heat in shock damper system instead of movement in the helmsman.

Robin, get some for the new boat! You'll be able to cruise along taking pictures when its rough!

RibRoy, Would love to hear Henrik's opinions on this. Sorry again for thread hijack, I've PMed JK to see if he'll split it.

Cheers

Tim
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Old 01 March 2005, 16:59   #26
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I would imagine that back injury or just discomfort from slamming along in chop is sometimes enough to put some people off ribbing/powerboating completely. I know I am 3 cm shorter than I was 10 years ago but thats probably just age!!!
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Old 01 March 2005, 17:02   #27
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Tim I understand what you are on about but I think you are looking at this the wrong way. The seats are designed to mitigate shock and you have to look at how the load (the weight of the person sitting on the seat) is applied to the seat and not the relative movement of the boat under the seat.

Nick already made the point that as the bow comes up you are shoved back and down onto the spring exerting a load acting parallel to the spring (compressing). If the seats were the other way around you would exert a load acting perpendicular to the spring (exerting a shear force but very little compressive force)

The way you are looking at the problem is as if the boat is exerting the load on the shock absorber and causing it to compress, however it is not the case. If there was nobody sitting on the seats while underway they would only compress slightly (under their own weight). However they will compress properly when loaded with the weight of a body. This shows that it is your own weight that causes the shock.

Another reason for the setup like this is that you are pulled slightly away from the console in the event of a stuff/ hard landing/ ploughing into a big one!! Otherwise you would be flung towards the console!!

Sorry to everybody that I have confused even more!!
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Old 01 March 2005, 17:24   #28
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Steve,

I agree totally about having to have the driver on the seat to make it work. For bikes, this is known as sag and is usually set to about 1 third of the total travel on medium - long travel bikes like mine.

Also the bit about being pulled away from the console for safety makes sense (although it would hardly be noticable), but then again you wouldn't want to be pulled away from the throttle !

I'm going to have to design my own suspended seat I think, then I can see for myself if I'm right or wrong...cos its making my head hurt now.

If the seats worked perfectly and were 100% efficient (obviously impossible), the helmsman would sit on the seat and wouldn't move in relation to the earth (assume a small see so the shock doesn't bottom out). The hull would move underneath and, in an ideal world would be free to move however it pleased. If the suspension system restricts this natural movement, energy will be transfered to the helmsman (not good), instead of being absorbed into the shock (which is what is wanted).

This is an interesting discussion.

Tim
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Old 01 March 2005, 19:18   #29
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....but if the seat absorbed all the energy the damper would likely get more than a bit hot.
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Old 01 March 2005, 19:59   #30
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Quote:
Originally Posted by jwalker
....but if the seat absorbed all the energy the damper would likely get more than a bit hot.
Bum warmer?
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