A bit o/t, but your pic reminded me of the anodes in my engine exhausts.
Agree with that entirely. Having had a chance to use my Seakeeper gyro extensively recently, it is clear that on my boat at least, the effect of the gyro reduces significantly with speed. At rest it performs to its optimum, at displacement speed the effect reduces with speed and at planing speed there is no discernable effect. I was looking primarily for zero speed stabilisation and ease/cost of retrofitting so a gyro made sense but if I was specifying a boat from new, I would go for fins if the option existed. In fact in an ideal world you'd probably specify fins for stabilisation at speed and a gyro for stabilisation at rest because one thing the gyro does have in its favour is practically no noise or vibration plus of course its never going to walk the boat forward in the middle of the night!
Humphree fins now address that, by turning 180° during zero speed operation.
I've not heard about this effect. Is it an issue on some boats?
It is on every fin stabilized boat in some conditions, i.e. whenever there isn't at least a gentle breeze, because the fins movements have always the side effect of slightly pushing the boat forward.
(yep, Humphree score low in my book on freedom of speech ): https://www.youtube.com/watch?v=EjFEoynDPwI In contrast, your sleipner fins will be near silent, even in the master cabin when you're right beside the actuators. Care to expand on that?
Good idea jfm. I'll ask the question.
Yup Magnum, all fin stabbed boats walk forwards at anchor, but only in some conditions. Mainly in places like Villefranche where you can get swell (hence stabs running hard) and little wind (so boat isn't pushed back on the anchor chain). You just need to be aware of it but in my book it is a tiny issue and not worth worrying about. I discovered it early on, on my first finned boat in 2011, yet I have stuck with fins since then (because as you say they are far better than gyros underway) and I'd spec fins on any new boat in the future. It's a tiny issue and never happens if there is a breeze to hold the boat back.
Electric fins can in principle rotate 180 deg to avoid this but that small advantage in no way compensates for the big noise levels in electric fin gearboxes, which will be with us until/unless different gearboxes become available. CMC have done better in this regard than Humphree imho. Here's a video in relation to which Hump threatened legal action against me this summer then shut up when I showed them I have an even worse one that I haven't yet published
The only thing to remember is that all this gear needs maintenance and Princess are vary capable of putting fin actuators under the bathroom floor and placing a bathtub or stone tiled mosaic shower above, with zero access hatches. I'd check this if I were you: I have a friend whose bathtub/mosaic tiles are being taken out today on a Princess 82 because the Trac fin under the bath needs maintenance. You just gotta hope whichever yard you pick puts it all back nicely. The labour bill, which I've seen, is pretty punchy. On my boat the fin actuators are both fully accessible by lifting floor hatches and removing one cupboard which was specifically made removable in the first place, and this is what you need imho if you plan keeping the boat > 2years.
That's some nice lateral thinking indeed.
It also begs the question why, if electric fins are driven by electric motors, hydraulic fins cannot be driven by hydraulic motors instead of hydraulic rams in order to be reversible. Yes controlling the precise movement of the hydraulic motor will be more of a problem but not insurmountable and the size of the motor might be an issue but it would get over the walking forward issue with fins driven by hydraulic rams and hydraulic motors might be quieter than either electric motors or hydraulic rams
Alas it wouldn't work Elessar.
If using hydraulics it's probably easier Mike to use rack and pinion, with racks long enough to create say 270 degrees of fin rotation. Controlling the angular position of a classic hydraulic vane motor is pretty difficult and an electric system would stabilise the boat much better I expect. Also hydr motors tend to need axial length to get high torques, which increases installation height. If walk-forwarding was a big problem then people might accept the downside and cost of these solutions, but it isn't.
Yes rack and pinion is one way but a reduction gearbox would be another. Yes controlling the angular position is an issue which is why I mentioned it but with a low geared reduction gearbox and an electronic control system it should be possible
Again correct. They do tend to be quite tall which again is why I said the size of the motor might be an issue. Yes I accept your point re walking forward not being a big issue. Having anchored in Villefranche many times in the last year, I cant say I've seen loads of fin stabilised mobos wandering all over the bay and crashing into each other
Well, I only read a review of the DMS thing, and I have zero first hand experience on them, so for all I know they can well be an awful product for whatever reason.
Its radical but is it scaleable down to smaller boats? And then what sort of cost would it be relative to the cost of a smaller boat? And would any production builder be willing to fit it on one of their grp hulls? How much drag would it create on a planing hull? My guess is that DMS know already that this system wont scale down which is why they're aiming it at the 30m+ market and my guess displacement steel boats only
