Ullman Seats

RibRoy · 01 March 2005, 17:03

Here is my Ullman Compact seats with the new fundament.
Ready for shipping to Tornado. Cant wait to test them !

Roy

Nauti Buoy · 01 March 2005, 17:09

They look superb, should be very comfortable with the suspension system in them. Very hi tec.

Nick Hearne · 01 March 2005, 17:15

Look very nice

One thing, put your finger in one of those holes when you are bouncing up & down & I ges it will chop it wright off!

Nick

slimtim · 01 March 2005, 17:46

I'm not questioning Ullman's design but I would've done the linkage bit the other way around.

Imagine the person on the seat staying where they are and the boat moving underneath (as it should). At present the boat will move up and FORWARD. With the linkage the other way around, the boat will move up and BACKWARDS.

Surely up and backwards is better...I'm applying principles used when designing mountain bike rear suspension, but essentially its the same.

I'm sure Ullman know what they are doing but would be interested to hear people's views.

EDIT: the linkage only allows the boat to tilt bow down transom up...if you see what I mean. With the linkage the other way around the boat could tilt bow up transom down, which is obviously more natural.

Cheers

Tim

jwalker · 01 March 2005, 20:29

Nope, I don't.

slimtim · 01 March 2005, 20:44

Ok, here we go. This is my best shot at trying to explain it.

The blue arrow indicates the direction at which I think the boat would move if the seat stayed where it was. I'm thinking that this allowable movement is un-natural to the movement the boat will actually make when hitting waves at speed (it will want to go up and back...like a mountain bike wheel hitting bump in a track when travelling at speed). The green arrows show how the hull would naturally pivot with this linkage (kind of). Pink arrow just shows that the shock can only compress, from its fully extended position...obviously.

Does that explain what I'm on about? Am I talking sense or is it all crap?

Sorry about going slightly off topic RibRoy, perhaps JK can start a new thread.

Great looking seats by the way!

Cheers

Tim

Nauti Buoy · 01 March 2005, 20:51

Quote:

Originally Posted by slimtim

Does that explain what I'm on about? Am I talking sense or is it all crap?

Actually that does make sense, but would the console in this case keep getting shoved towards you as in theory you and the seat would not move but the Rib would move towards you....... not you've got me at it too so "Am I talking sense?"

slimtim · 01 March 2005, 21:02

woohoo! Someone who almost agrees!

I think in this case, the console would effectively seperate from you slightly (how much depends on the starting angle of the linkage). If it was the other way around the console would appear to come towards you (ie the boat would move backwards underneath you).

Imagine a set of front suspension forks on a mountain bike. When you hit a bump (similar I think to a RIB hitting waves) the line at which the front wheel axle takes is up and back (because the forks at angled backwards). This, i think is roughly the ideal path for the axle to take. So you can model the bike wheels as the hull etc and the rider/bike frame as the helmsman/seat cushion on the RIB.

The actual movement of that linkage I have drawn could be pretty complex depending on the sea movement etc, but I reckon it would absorb bumps better with the link the other way around. As I said before, I'm sure Ullman know what they are doing so there must be a good reason why they have done it like that. Any ideas anyone?

Cheers

Tim

Nick Hearne · 01 March 2005, 21:05

As you hit a wave the bow comes up, pushing you back & down (or boat comes up) this will compress the spring

Will it not!
Think what happens when you are say standing up holding on as you hit a wave, you are forced back & down (or the boat is coming up so feels like you are!)
Still think the holes are bloody dangerous!
Nick

slimtim · 01 March 2005, 21:06

RibRoy,

I've just noticed, do the seats rely on flex in two carbon fibre plates instead of beams and linkages? It looks that way from the pics...very interesting, no pivots to maintain/seaze.

Tim

robin · 01 March 2005, 21:14

Quote:

Originally Posted by slimtim

Ok, here we go. This is my best shot at trying to explain it.

The blue arrow indicates the direction at which I think the boat would move if the seat stayed where it was. I'm thinking that this allowable movement is un-natural to the movement the boat will actually make when hitting waves at speed (it will want to go up and back...like a mountain bike wheel hitting bump in a track when travelling at speed). The green arrows show how the hull would naturally pivot with this linkage (kind of). Pink arrow just shows that the shock can only compress, from its fully extended position...obviously.

Does that explain what I'm on about? Am I talking sense or is it all crap?

Sorry about going slightly off topic RibRoy, perhaps JK can start a new thread.

Great looking seats by the way!

Cheers

Tim

Tim....I am no engineer but I know what you are getting at here, you'd prefer a different colour wouldn't you?

jwalker · 01 March 2005, 21:15

Considering a load on the seat: if the bow rises and the stern is the fulcrum there is compressive load on the spring. If the stern rises and the bow is the fulcrum there is compressive load on the spring. If both the bow and the stern rise there is compressive load on the spring. And all moments between bow and stern will cause a compressive load on the spring. Only if the bow goes up/down and so does the bow/stern, so as to pivot directly under the spring, is there no compression of the spring but in that situation you wouldn't need it. The fore and aft movement of the load due to the arm pivoting is unlikely to be a problem. Imho, of course.

Nauti Buoy · 01 March 2005, 21:19

Quote:

Originally Posted by jwalker

Considering a load on the seat: if the bow rises and the stern is the fulcrum there is compressive load on the spring. If the stern rises and the bow is the fulcrum there is compressive load on the spring. If both the bow and the stern rise there is compressive load on the spring. And all moments between bow and stern will cause a compressive load on the spring. Only if the bow goes up/down and so does the bow/stern, so as to pivot directly under the spring, is there no compression of the spring but in that situation you wouldn't need it. The fore and aft movement of the load due to the arm pivoting is unlikely to be a problem. Imho, of course.

Well now I understand..........

smokie · 01 March 2005, 21:28

Whatever ... Its an improvement over non-spring seats.

RibRoy, lets us know how you like them. I'm planning on get a 7m rib someday and I'd like comfortable seats.

robin · 01 March 2005, 21:28

There is only one alternative......fit these instead

slimtim · 01 March 2005, 21:29

haha, lol at Robin! Yeah, if I designed it, I would specify some pimpy zebra stripes or something!

Nick and Jeff, there is no doubt that the shock/damper system will compress however the hull moves underneath (unless the pivot is where the shock meets the hull as Jeff said...but this wouldn't be a problem as it would be like a node of oscillation) and there is no doubt that it would have a significant effect on increasing driver comfort. It just that I don't think the path at which the unsprung mass (hull etc) can take is ideal.

Imagine the suspension fork on a bike again. If mountain bikes were designed with the headtube angle the other way (so the forks pointed backwards), then the forks would absorb bumps but not nearly as affectively. Lots of energy would still be transfered to the rider. The bike would also look crap and handle like a dog.

hhmmm, if only I could apply this much imagination and thinking to my uni project!

Tim

Nauti Buoy · 01 March 2005, 21:34

Quote:

Originally Posted by robin

There is only one alternative......fit these instead

I guess you are as lost as I am, I think they are a smart looking seat, probably a major finger hazard, but as for the logistics of which way the seat will rise or fall when the bow goes up or down has hopefully been taken into account as they don't look cheap.

slimtim · 01 March 2005, 21:36

They look superb don't they

jwalker · 01 March 2005, 21:36

Quote:

Originally Posted by slimtim

Imagine the suspension fork on a bike again. If mountain bikes were designed with the headtube angle the other way (so the forks pointed backwards), then the forks would absorb bumps but not nearly as affectively.
Tim

Yer reckon. Try pushing a wheelbarrow up a kerb and then try pulling it up the same kerb. A bike is different because the forward lean of the fork makes the front wheel a castor, which is a bit essential for riding stability.

Nauti Buoy · 01 March 2005, 21:37

Quote:

Originally Posted by slimtim

hhmmm, if only I could apply this much imagination and thinking to my uni project!
Tim

Just a thought but perhaps this should be your Uni Project!!!