Stabilizers for Blue Angel, engineering question
- Thread starter BartW
- Start date
BartW
Well-Known Member
thanks for posting your experience,
where do you sail / anker now ?
any idea of the size of your fins ?
I know your boat is smaller / not compare-able, but just out of interest.
BartW
Well-Known Member
this would be a very simple solution, very temptings as it is all DIY, which I like as you know,
but I'm with Jfm on this, I believe we may not underestimate the magnitude of forces at planing speed.
the GRP of the hull where the hi lo platform is fixed is approx 25mm thick,
I experienced the strength of this,
a reinforcement of the hull until total thickness of 79mm, would create a extremely solid surface, compared to 25mm GRP + stringers,
(on condition that these add on layers are well bonded with the old surface as you highlighted)
imo
BartW
Well-Known Member
in this yard:
http://www.chantiernavaldesbaux.com/
I made a appointment for the next liftout, antifouling, replace 2 seacocks , and place some UWL's (sorry for this
)dates are not yet firmly fixed, planning was early april.
want to go there within 2 weeks to discuss about the stab project.
which yard have you seen ?
perhaps you've seen another interesting place ?
BartW
Well-Known Member
all agreed,
yes will post all progress here,
this thread gave me a lot of usefull info, and enhanced my vieuw on the project,
much more then I expected !
in 2 weeks, will be a long weekend on the boat,
will take many different measures, in function of what has been discussed on here.
vas
Well-Known Member
Bart, following your suggestion, just posting here my comment:
I'd think that from an engineering pov, you really want to distribute all bending/torsional etc forces as much and smoothly as possible.
So I'd have thought that a good approach would be that your reinforcement patch should reach and bind properly and securely to BOTH the stringer (towards the keel) and the chine (outwards) This way the "nerve" of the chine and the stringer can absorb and distrubute forces much more efficiently and with less stress to the hull. That's with my half baked engineering hat talking...
cheers
V.
I'd think that from an engineering pov, you really want to distribute all bending/torsional etc forces as much and smoothly as possible.
So I'd have thought that a good approach would be that your reinforcement patch should reach and bind properly and securely to BOTH the stringer (towards the keel) and the chine (outwards) This way the "nerve" of the chine and the stringer can absorb and distrubute forces much more efficiently and with less stress to the hull. That's with my half baked engineering hat talking...
cheers
V.
MapisM
Well-Known Member
LOL, nope, actually I guessed that you were thinking to use that one!in this yard:
http://www.chantiernavaldesbaux.com/
I made a appointment for the next liftout, antifouling, replace 2 seacocks , and place some UWL's (sorry for this
dates are not yet firmly fixed, planning was early april.
want to go there within 2 weeks to discuss about the stab project.
which yard have you seen ?
perhaps you've seen another interesting place ?
We were together when you met the owner, while we overnighted at Sanary s/m during the FdC...
And as I said, the first impression I had was not bad at all - though it's just an impression, of course.
While you will be there, you might try to ask what they would suggest (particularly for the hull strengthening) also to the much bigger yard which we saw right in front of a small bay, where we anchored for lunch (sorry, can't remember the name).
Actually, they seemed to deal only with very big stuff, in the superyacht league, so probably a bit of overshooting even for BA.
But they surely have a good experience with fin stabs, which are rather the norm than the exception, on very big boats.
Forty_Two
Well-Known Member
610mm x 610mm so 0.37sq m and are plenty powerfull enough for our size.
We are based in La Napoule & have cruised to Barcelona, Elba (the coastal route) & Corsica direct (12 hrs for us slowcoaches) and pretty much all in between.
Pretty much stay in ports these days although St Cross is a fav anchorage & one of the few with less boaty swell. We have a set of the Magma flopper stoppers which help a bit together with our steadying sail to stop us swinging about too much.
Good luck with the project, it is a daunting one as so much space is needed for the ancillary kit but totally worth it & as Piers says it's almost priceless in terms of the effect. I was hoping it would be good but in fact the difference is staggering, way better than i hoped. It's not having to turn into big boat wash that's so nice, just leave her on autopilot & go up & down instead of rolling on your beam ends!!
BartW
Well-Known Member
I have to hurry with this project, because every day I notice I 'am getting older,
now severe symptoms of memory loss
that's a subsidery of monaco marine,
indeed very big, have been in there ones, appeared like village.
I'm sure there is quite some know how, and experience in there, but then I have to find the right entrance.
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MapisM
Well-Known Member
Actually, while I agree with J that BA is in a different order of magnitude vs. my and 42's boat, the reason has much more to see with her displacement than with her speed.
Also the CMC engineer, when we spoke of current absorption, confirmed me that:
a) the higher peaks are created by the zero speed usage, and
b) the average current necessary while cruising is much lower.
Now, it's pretty obvious that the higher the current absorption, the higher the forces the electric motor is fighting against.
We didn't discuss the difference between low and high speed, but I would dare guessing that the need for stabilizing effect actually DECREASES with speed.
Otoh, of course the drag increases, but that's a constant force, along the direction which the fin is designed to cut through, rather than contrast. It can't be too bad, otherwise the fuel burn would skyrocket.
Just think about it: at anchor, the fins action is akin to two big hands, which grab the fin shafts and keep the hull stable whenever a wave makes her roll.
Or, seen from another viewpoint, which could grab the fin shafts and make the boat roll back and forth real bad, even in flat water.
Now, these are big forces! To me, it's pretty obvious that the fin shafts must bear more transversal than longitudinal forces.
Also for that reason, I'd rather exploit the stringer strength, than cut it to make thicker a larger area.
I agree with Vas that if on the external side of the shaft holes there aren't other stringers, but directly the keel, that's also a structurally strong area, which could nicely contribute to create the fin supports.
MapisM
Well-Known Member
ROTFL, welcome to the club. But beware, the president chair is already taken by myself, as the founder...!
Yep, spot on re. the other big yard.
D
Deleted User YDKXO
Guest
Oh blimey, Bart, take a cold shower and have a lie down. Its an awful lot of money to be spending
BartW
Well-Known Member
I completely agree with you / CMC that more power from the motors is required at anker,
and very little power / movement of the fins is needed at planing speed,
but I am mainly thinking about sudden big waves touching the fins, (in random directions)
which can have even more impact on th fins at speed,
that will create the most stress / forces on the system and the hull.
BartW
Well-Known Member
there is one small benifit Mike,
some folks invest their savings in bonds or any other risky investment, and have sleepless nights about the profit, or eventually loosing some money.
OK I could invest in safe things such as houses (which I do),
But my mind is OK and at rest with the the fact that I'll be loosing the money spend on the boat,
and at least I've had the fun with it, and my private satisfaction
D
Deleted User YDKXO
Guest
€50 and a trip to Amsterdam would be a lot cheaperand at least I've had the fun with it, and my private satisfaction
jfm
Well-Known Member
That big yard in your pic is Monaco Marine, at La Ciotat. They seem to do only superyachts. For example, they removed Mirabella 5's mast a few years ago for her 4 year reg check - major stuff. CN des Baux seems good. They have a nice list of credentials, including the CNB Hamilton II - she has a v knowledgeable owner
jfm
Well-Known Member
Thinking further about these electric stabs, i think you need to look into heat dissipation BartW. With hydraulic stabs, this isn't an issue because underway the prime mover (main engines) are seawater cooled and on at-anchor dutythe prime mover (10hp electric motor) is cooled by the usual shaft fan and fins. In addition, there is seawater cooling to the hydraulic oil, which cools the system
But in the CMC case you will have say 3Kw each side in an enclosed space under the bathroom floor. You cannot ventilate the air easily becuase bilge air can be smelly. I would therefore be quite concerned about heat. 3Kw of heating rate each side is obviously not trivial at all. This is worth asking the suppliers about and worth getting warranty protection on, imho
But in the CMC case you will have say 3Kw each side in an enclosed space under the bathroom floor. You cannot ventilate the air easily becuase bilge air can be smelly. I would therefore be quite concerned about heat. 3Kw of heating rate each side is obviously not trivial at all. This is worth asking the suppliers about and worth getting warranty protection on, imho
BartW
Well-Known Member
good point,
average diss at navigation is not high,
but with a swell at anchor could be important
Absorbed power both fins
(underway mode)
Average power 350 W
Peaks power 750 W
Absorbed power both fins
(anchor mode)
Average power 2.5 kW
Peaks power 6 kW ( for t < 0.2 s)
A fan and a hose as used for your genny ventilation in M2 could be a very cost effective solution
with these figures, I could probably test to run them from 2 invertors, (with the battery's behind to cope with peak power)
depending on the max contunious power of the engine alternators ofcause
BartW
Well-Known Member
€50 and a trip to Amsterdam would be a lot cheaper
you have'nt met my swmbo yet I believe
wakeup
Well-Known Member
Bart, I find that if you drink the right amount of rosé you don't notice the swell as much in SoF. You can buy a lifetime of rosé for the price of a new set of stabs.
