ICC: What's the actual 24m limit?

[jfm]

Ah right, i'd missed that.

Having said that, it seems to me nowadays that most boats over about 70 feet are expected to run the genny 24/7 when away from port?

It does seem that way Nick, but its mostly becuase virtually all the Italian builders have for years, now followed by many others, insisted on fitting 230v fans to vent the engine room. My boat retains 24v fans (even though they draw 65 amps) and if it didn't i would have specced them. Obviously, 2 engine alternators can do the 65amps plus the other 24v loads with ease while underway. I therefore do much underway running without the gensets, and only flick the gensets on for cooking and the kettle when underway.

But you're right: most do run gensets, and Fairline/uk builders (good on 'em) are the intelligent exception

 

[Nick_H]

It'll be interesting to see how much effect the gyro has at higher speeds (though far less than fins for sure). From the earlier gyro thread:

They also worked well when doing 20 knots in a 2.5 - 3m quarterly sea.

 

[wakeup]

Do they also fit fins for fore and aft movement as well as roll. I am thinking maybe two winglets at BT height and position could provide enough moment to correct the fore and aft movement or would it be over kill on an already finned boat?

 

[jfm]

It'll be interesting to see how much effect the gyro has at higher speeds (though far less than fins for sure). From the earlier gyro thread:

Yes it will. Thing is, seas are not at all the same. A 2.5-3m quartering sea can be lots of things, as you know. If the wave period is shortish, the gyro could work well, becuase in that circumstance its limitation of a limited precession stroke may not hinder it too much

I'm referring to the fact that it only resists roll as it precesses, and mechanically the seakeeper can only precess +/- say about 75 degrees from the midpoint, so when it's done all that stroke it has no more to offer and indeed as it returns to centre (ready for the next wave) it is adding to the roll, which of course means the makers don't let it return to centre with any speed. In contrast, a fin has no stroke limitation and can hold a boat at an angle to the sea surface all day long in a steady state. The other limitation with a gyro is that the more anti-roll force you get from it the shorter a time period it can do it for. you get more antiroll torque if you let it precess fast, but then you run out of angular stroke faster. A fin doesn't have this problem - you can have the max antiroll force that the fin can give, all day long.

It's complex stuff and wave shapes are so complex that you just cannot generalise. It will be good to hear reports from your boat when you get it all done. You can of course flick the gyro on/off at the flick of a switch (the spool up time is not relevant here) just like fins, so you'll be able to carry out good with/without instant comparisons when the boat is at sea. Lookimng forward to hearing about it!

 

[jfm]

Do they also fit fins for fore and aft movement as well as roll. I am thinking maybe two winglets at BT height and position could provide enough moment to correct the fore and aft movement or would it be over kill on an already finned boat?

You mean pitch? Theoretically possible and some 4-fin systems have a slight bit of antipitch built into the software but the limitations are huge. In a big sea the forces to overcome bow lifting on a wave are massive and anyway you don't want the stab ultimately to win because it could sink the bow. you end up therefore with systems taking just a tiny bit of the pitching motion away, but in reality hardly anything at all. In reality, stabilisers take out roll and nothing else, but that is a major benefit to comfort and seasickness

 

[wakeup]

yes pitch, couldn't think of the term this am, brain not working , and I have a PPL so should know the term

May be a half way house system that dynamically controls the tabs in concert with the stabs to reduce some of the pitch could be possible.

 

[jfm]

Yes indeed. Sleipner are contemplating a fin stab system that integrates control of the tabs and rudders (autopilot), which when separate (as currently) tend to "fight" each other a bit. You could go a step further and add a 4 fin ssytem too. With some or all of this, could reduce pitch a bit. But still, as the bow of the boat goes into even a modest wave (say 1m) the buoyancy forces at the bow are monumental if you keep the bow from rising, even allowing for a bit of stern lift with the tabs. So you will only ever take out a little bit of pitch, and nothing like the 80% you can take out of roll.

 

[wakeup]

Ok so if rudders were moveable independently together with the tabs you could have a form of advanced manoeuvring as well e.g crabbing the boat if all rudders and stabs point the same way or rotational if opposite etc etc.

 

[MapisM]

My boat retains 24v fans (even though they draw 65 amps) and if it didn't i would have specced them.

Why, J? Couldn't you feed the fans out of the inverter(s)?
Besides, you don't need variable speed for the fans, and nothing can beat AC electrical motors in terms of reliability, anyway.

 

[MapisM]

Ok so if rudders were moveable independently together with the tabs you could have a form of advanced manoeuvring as well e.g crabbing the boat if all rudders and stabs point the same way or rotational if opposite etc etc.

LOL, what's next, using fins as oars to get rid of propellers...?

 

[wakeup]

If you flap them quickly enough

 

[Balearick]

Do you suffer when underway, or just rolling about at anchor? If the latter, then I think a gyro is worth considering, although I wouldn't buy one without spending a day on a gyro equipped boat, to make sure it really does solve the problem for you.

Only at anchor. Underway I'm fine (as long as I'm at the helm - same as car drivers rarely get car sick, it's always the passengers). I don't even mind choppy seas underway, in fact riding up a big wave to splash down the other side and soak the guests is great fun with the ABS 45

So gyro seems better for my purpose, but also as I want to keep the ability to do 35+ knots, fins would create drag.

 

[MapisM]

I want to keep the ability to do 35+ knots

In this case, don't even consider fins, imho.

PS: I'd be careful in the boat choice, though.
If for instance the T58 only allows gyros to be placed fully astern, that's never a good idea in a planing boat.
I know that placement flexibility is "sold" as one of the gyro advantages, but they only consider the stabilization effectiveness, ignoring (purposedly) the negative effects on the boat cruising attitude of moving astern the hull CoG.

 

[Balearick]

In this case, don't even consider fins, imho.

PS: I'd be careful in the boat choice, though.
If for instance the T58 only allows gyros to be placed fully astern, that's never a good idea in a planing boat.

I'd imagine the only place for a gyro on the T58 would be in the stern crew cabin. But I'm not sold on the T58. I'm still considering at least 4 other open boats including:

- Absolute 64 (new)
- - pros: Love the IPS drives, good open layout, good garage. Possible space for gyro in engine room.
- - cons: Only a couple of saloon windows open, boat design is a bit square, master & cabins a bit "ikea" for my taste.

- Targa 58 (new)
- - pros: Love the helm, salon, cockpit and cabins - the best helm I've seen, love the open windows, love the disappearing patio doors, great master and heads. Definitely got "vavavoom".
- - cons: No garage, useless -for me- crew cabin, huge useless crew cabin window across the stern right where the boat name wants to be, no VIP cabin, no IPS drives (pity!). Gyro probably only fits in stern crew cabin.
(additionally someone close to Fairline told me Fairline are having trouble with those power-away patios doors and could stop offering them)

- Couach 28m (used)
- - pros: Beautiful shape, huge open salon, great helm, fabulous garage.
- - cons: Huge. Will probably cause problems with Med police and my ICC. Will probably need a lot of work. Will double my marina bill.

- Princess v62 (new)
- - pros: Beautiful shape, elegant salon, nice cockpit, great garage.
- - cons: salon windows don't open (except one small one), helm is featureless and dated, furniture looks from early 90s, no T58 "vavavoom" here.

- SS Predator 60 (new)
- - pros: Nice shape, nice salon, nice garage, pod drive/Arneson surface drives
- - cons: salon windows don't open, furniture a bit dated, no T58 "vavavoom".

I also liked Baia Italia 70 but it's too expensive (no used around).

 

[jfm]

Why, J? Couldn't you feed the fans out of the inverter(s)?
Besides, you don't need variable speed for the fans, and nothing can beat AC electrical motors in terms of reliability, anyway.

Yes, ac and inverters is perfectly feasible, but kinda unnecessary. I don't like to use inverters if not needed. I don't accept the reliabilty comparison becuase (i) the choice is not DC vs AC motors but rather just DCmotors vs a combo of inverter+ACmotors, and while I dont have data I suspect the reliabilty is then the same. Anyway I have multiple fans so they wont all fail together; there is redundancy in the system

But I'm not making a strong fight here - the differences are marginal and hardly worth worrying about

 

[MapisM]

the choice is not DC vs AC motors but rather just DCmotors vs a combo of inverter+ACmotors, and while I dont have data I suspect the reliabilty is then the same.

Well, actually the choice is "just DC" vs. "inverter(s)+AC, or genset(s)+AC".
I suppose that a failure of all inverters and gensets is rather unlikely, though I also don't have any stats...

But I agree, we're not talking of differences worth worrying about.
I only asked because I understood that you had some "strong" reasons for speccing 24V fans, but couldn't think of any.

 

[Hurricane]

Balearic, have you thought about buying a with stabilisers? These have an amazing effect in eliminating motion. There is little stock of used boats so it likely would have to be a new boat, or you could get them retrofitted to a used boat (Osmotech are gearing up to retro fit Sleipner stabs)

Sleipner are just about to put a vid on Youtube showing a split video screen of my boat with left/right of screen with/without stabs and you'll see how good they are (I have seen the video in draft in last couple of days)

They would be about £100k to retrofit to a Sq74 or 78 but if you take that into account in your budget it could make sense. Osmotech have specifically considered (in the last month or so) on a customer boat the retrofitting of stabs to a Sq78 but obviously there is a wide range of boats that they can bee fitted to

The video is on the Sleipner stand at SIBS - rolling loop on a big screen

 

[grumpy_o_g]

The video is on the Sleipner stand at SIBS - rolling loop on a big screen

Rolling loop is perhaps an unfortunate term...

 

[Balearick]

- Couach 28m (used)
- - pros: Beautiful shape, huge open salon, great helm, fabulous garage.
- - cons: Huge. Will probably cause problems with Med police and my ICC. Will probably need a lot of work. Will double my marina bill.

A little update on this...

I am now in Antibes, home of the Couach 28m that sparked off this thread's question. The agent told me today it's just been sold... oh well. I'm not too sad because I think I would have run into trouble at some point. I can imagine explaining to a boat full of med police how to measure and calculate "LLL" to squeeze under 24m...

However agent was quick to point me to an SS predator 72, also lying in Antibes, and I must say it's quite gorgeous... Swmbo thinks so too... I'll check it out next week (quite likely though I won't buy a boat until I have a clear route to sell my ABS 45).

 

[scej]

I have delivered a few boats with both gyro stabilisers and conventional fins. As far as I was concerned the gyro seemed to have little or no effect when underway and some benefits at rest, this was a single unit situated in the stern. It's a big lump of kit so some thought would need to go as where to fit anywhere else.

The conventional fin type seem to work by far the best IMHO, as far as sped is concerned we tested one boat with the engineer before we left to look at parameters and we clocked 38 knts with them on when they where fixed the speed dropped by about 1/4 knt it should be noted that at speeds in excess of 30knt they should be centred as they can create some interesting moments when turning.