Stability at rest

[Vromme]

I was out the other day in typical slop running side onto the current/boat and a 5.2m quintrex (freedom something or another) anchored nearby. I noticed that his boat was rocking around considerably more than mine. I have a 5.2m sea devil (23degree GRP but flooding keel, 200odd litres/kilos as ballast). The quinny didnt look like it had a steeper than average quinny deadrise. He had similar setup re motor/fuel/extras and 2 guys in it (like me). I think it was mainly due to the fact of the weight (my hull alone is over 600kgs + ballast). It could have been those particular conditions that his boat didnt agree with, there really was no comparison in stability between our 2 boats.

I have also noticed a lot of game boats with larger top decks/towers that can also really wallow around under anchor/drift (obviously due to centre of gravity).

It got me thinking it must be possible for someone to come up with a device that can measure movement at the centre of a boat. You would probably need to setup some sort of bench mark in terms of a raft of some kind so you can allow for variation in swell etc. You would think this (or something similar) could also be used to measure impact whilst travelling (ie softness of ride at a variety of speeds).

How good would it be to be able to get a number or percentage for stability and softness of ride rather than the current method of opinion and guess work.

Any engineers out there who could invent something? Dont think youd get rich off it but would make a lot of boat buyers happy and probably lots of manufactures unhappy! Also put an end to a lot of arguments and possibly start some new ones.

[The Woo]

Static stability tests are already done on commercial and charter vessels.

Realistically, for private vessels, there's really too many variables. Wind and tide conditions, sea state, vessel loading, aall have a marked effect on boats, and some conditions suit one type better than the other.

I think trying to quantify stabilty into a "number" would be very difficult, WHILST satisfying the majority of manufacturers that the test is "fair", would be a hard slog.

[Jabba_]

Maritimo in stall big arse Gyro's into their top line boats.. The lower speced boats cam option up to get this gyro.... The Gryo weigh's about 1 tonne all up.. It inside a capsule that is secured to the hull, nears as possible to the centre off hull. Inside the capsule their is a weight that spins at a ridiculous speed.. It reduces a lot off rolling at rest, it also helps control the ride while under way.. If you have to ask how much it cost, then you can't afford it..It cost a fortune..

[wirlybird]

Its funny how that technology is perceived. get a standard bike wheel and hold it at the axle get a mate to spin the bike wheel and try and move the bike wheel sideways by pushing one hand away and drawing the other closer to you. The resistance will multiply the further away from center you get so it isn't really a gyro but a fancy heavy wheel using newtons first law to correct the vessels velocity.

[deckie]

Its funny how that technology is perceived. get a standard bike wheel and hold it at the axle get a mate to spin the bike wheel and try and move the bike wheel sideways by pushing one hand away and drawing the other closer to you the resistance will multiply the further away from center you get so it isn't really a gyro but a fancy heavy wheel using newtons first law to correct the vessels velocity.

hhmmmmmmmmm

[The Woo]

Gyro stabilizers are getting smaller and somewhat more attainable, if you have the fiscal means. They're BIG bucks, like $80 grand plus fitting for a small one suitable for a sub 40ft boat.

They don't advertise the masses of power they require to run them either, nor the warm up times (I've heard 3/4hr is typical).

But, if money were no object, and the vessel wasn't compromised in layout or access by fitting it, or hindered by the weight of the gyro and the support systems, I'd love to have one!

They're even fitting these into outboard powered boats in the USofA now.... I'm unsure how they're feeding the gyro power though.

http://www.youtube.com/watch?v=J1zVat8xuV8

[Jarrah Jack]

Didn't know you had a Sea Devil, Vromme. I tried to get one recently but gave up then two came on the market a few weeks later. Any pics? Even saw a Seydel on boatpoint last week.

[PinHead]

I was out the other day in typical slop running side onto the current/boat and a 5.2m quintrex (freedom something or another) anchored nearby. I noticed that his boat was rocking around considerably more than mine. I have a 5.2m sea devil (23degree GRP but flooding keel, 200odd litres/kilos as ballast). The quinny didnt look like it had a steeper than average quinny deadrise. He had similar setup re motor/fuel/extras and 2 guys in it (like me). I think it was mainly due to the fact of the weight (my hull alone is over 600kgs + ballast). It could have been those particular conditions that his boat didnt agree with, there really was no comparison in stability between our 2 boats.

I have also noticed a lot of game boats with larger top decks/towers that can also really wallow around under anchor/drift (obviously due to centre of gravity).

It got me thinking it must be possible for someone to come up with a device that can measure movement at the centre of a boat. You would probably need to setup some sort of bench mark in terms of a raft of some kind so you can allow for variation in swell etc. You would think this (or something similar) could also be used to measure impact whilst travelling (ie softness of ride at a variety of speeds).

How good would it be to be able to get a number or percentage for stability and softness of ride rather than the current method of opinion and guess work.

Any engineers out there who could invent something? Dont think youd get rich off it but would make a lot of boat buyers happy and probably lots of manufactures unhappy! Also put an end to a lot of arguments and possibly start some new ones.

not sure what you mean by the centre of the boat? on the deck or the hull..if at the exact centre point of the hull then every boat would be the same..zero movement as it is the pivot point...it can only go up and down on a swell and nothing else.

[johncar]

It is a great idea and no doubt been debated in certain circles. Getting everyone to agree to a standard test would be a problem and would everyone have faith in the results.
There are just so many variables involved to make it definative and other factors like a boat with good stability or ride results may be a pig in other ways like wetness, and broaching and general performance and handling isuues, and how do you standardise sea conditions??
A lot of customer favour comes from perceived ride and stability which is evident comparing GRP to Ally hulls as in the noise factor of water slapping on the metal hull is no doubt louder and yes it is often perceived as a rougher ride or rolling around more at rest so a customer may still prefer the quieter GRP although it's test results perhaps worse.
I guess I am trying to say that everyone seems to like different characteristics in boats and I see it just within my circle of boating mates and at the end of the day I think most of us manage to get something that we are reasonable happy with and I really doubt whether we would take a real lot of notice of a ride and stability rating alone. It would still involve puting the boat through it's paces where you can make a first hand assessment of these things, in conjunction with all else

[Moonlighter]

As an aside, one of the few times I have ever been seasick was when out at the Barwon Banks for an overnighter on a 6m Quintrex Offshore a mate of mine had for a (short) while.

Man, I swear that boat moved really weirdly in the seas we had that night. It seemed to slide around sideways and after an hour or two, I started to feel crook and before long the burley was flowing.... Ugly stuff and I wasn't even hit-and-missed. Done the same trip in the 4.8 m boat I owned then and in other boats in similar conditions and no dramas, it was definitely a Quintrex thing, millennium hull, hate them!

Cheers

ML

[Squidlet]

hhmmmmmmmmm

Deckie that's an absolute pissabud,my gut is killing!!
Cheers Chris.

[Vromme]

PinHead, good point, the device would have to be the same point on boats and I think it would need to be in the centre of the deck, even if it was only 100mmx100mm or less you could still measure side/forward/back movement.

Jarrah Jack, I bought the sea devil just over a year ago. I will try and pull my finger out and put some picks up (have to take some first!). Its a 2008 with 115. Very happy with it. It is significantly heavier/stronger than the older ones. I used to fish out of them often but think the newer ones feel even softer, very solid underway in chop/swell. I was thinking the seydel as well but the flooded keel of the devil really helps under pick. But who knows how much because there is no way of putting a number to it, you just have to take my word for it!

Northern Beaches Marine in Brookvale Sydney bought the molds (the 2nd 520 boat on their website is my boat when first built). I have heard good things about NB Marine and the guy they are using to build them. I hope they continue to build them well.

Those gyros look bloody great. If I ever bought a large game boat I would make sure I had a few $ set aside for one of them. Hell whats another 100k odd when you consider the costs of the boats not to mention ongoing costs birth/fuel/maint/gear etc etc.

[David Ambler]

Some years ago I had a ferro Hartley South Seas sloop. A deep full keel and heavily ballasted she weighed about 12 tonnes. I was anchored behind the wrecks at Tangalooma in gentle seemingly calm conditions with just a ripple on the water. Whilst every other vessel at the anchorage remained still my yacht developed a harmonic oscillation and was just about rolling to her beam ends. It looked quite weird to see her rocking from side to side when everything else there was as calm as a duck on a pond. Sold her in 1987 after many good adventures.

[wirlybird]

hhmmmmmmmmm

ha ha ha sorry i have a shocking capacity for explaining things but a great capacity for understanding them. Try this link first

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

[deckie]

lol wiirly, maybe its me i dunno. I was reading it and thinking "am i stupid or something ?" Never much liked physics though ;D
Just an excuse to see a smokin hot Pauline, that woman is the sex bomb.

[wirlybird]

OMG thats wrong. have you been waiting for the right moment or what ha ha ha

[Jabba_]

hhmmmmmmmmmHey Deckie, thanks heaps for that picture of Pauline.. It was a good help last night. lol

[deckie]

Yeah glad to help jabba...i've found it damn handy on the odd occasion, nestled up the end of a quiet bay with noone around, birds chirping, mullet jumping...its a romantic setting i wont share with anyone but Pauline.

[Vromme]

Its funny how that technology is perceived. get a standard bike wheel and hold it at the axle get a mate to spin the bike wheel and try and move the bike wheel sideways by pushing one hand away and drawing the other closer to you. The resistance will multiply the further away from center you get so it isn't really a gyro but a fancy heavy wheel using newtons first law to correct the vessels velocity.


I think this is what you were trying to get at whirly.

http://www.youtube.com/watch?v=pF_SUvPAOSs&feature=related


I still think Pauline may have a problem getting her head around it!

[wirlybird]

thats it crazy times had by all

[deckie]

I still think Pauline may have a problem getting her head around it!
Yeah i see where you're going with that ;)
Thats some wild and crazy stuff vromme...just look at the face on the dude near the end.
But, But, i cant see a bicycle wheel ever replacing quality porn.
What were we talking about ?