Med Speed Loss

[Deleted User YDKXO]

Back in January when I first got my boat in Mallorca, it achieved a flat out speed of 31.5 knots (GPS measured). By May the boat had been moved to the Cote d'Azur and the max speed had dropped to 26 knots with a 300-400 rpm reduction in max rpm. I arranged for a diver to clean the hull and I can see that that he has removed most of the fouling from the hull although the sterngear is not absolutely clean. Dissapointingly, the max speed has not increased after the hull cleaning which leaves me a bit puzzled
Question for Medxperts. Does increasing water/air temperature affect boat speed? Or, is it still likely to be due to hull fouling or some other mechanical problem?

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[longjohnsilver]

Bring it back to the colder UK climate and it WILL go faster, something to do with the density of air, the colder it is the better the engine goes. However I would get someone to clean your strengear, that's most likely where the main problem is. Find yourself a decent diver ;-))

You SoF peeps, speed, speed, speed......................../forums/images/icons/smile.gif

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[DavidJ]

Temperature does have a negative effect ( engine power is proportional to the expansion ability of air so the colder in and hotter out the better) but for me I haven't noticed any difference. Hull cleaning did make a huge difference for me last year and I'm surprised that you didn't notice an improvement. The fact that both engines have dropped eliminates (statistically) a mechanical problem so back to the hull and the sterngear again is my guess. Have a snorkle under and see what sort of a job he did.
David

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[Deleted User YDKXO]

I have been snorkelling under the boat every day for the last 2 weeks actually (joys of the Med as oppposed to the Channel!) and the hull looks fairly clean although, as I say, the sterngear is a bit manky. I think you're probably right about the sterngear
I had the option to lift and scrub the boat but the yard wanted Euros1000+ compared to Euros300 for the diver
How does fouling go in the Med? Does the growth slow down from now on?

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[Deleted User YDKXO]

How about me buying you a cheapo air ticket and you doing the job then, John? I might even throw in a beer or seven
As for speed, at about £3/gal for go-juice, I'm looking to get every last knot

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[martynwhiteley]

'Mechanical' problems may still be a cause.

It is likely that if either fuel or air filters started to block up, they would do so in tandem.

Other causes could be some new soundproofing or blockage to air intakes reducing the amount of combustion air available.

Possibly quality of fuel.

Also it is possible (depending upon type) that the control system is now not pulling full throttle.

Could a different hood configuration be causing more drag?

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[Russell]

We've had a boat on the Costa Brava for the last couple of years, and the fouling has been a nightmare, especially on the metal bits. Unfortunately the boat is left unused for up 2 a couple of months at a time, and twice we've had 2 have it lifted out to clean the propshaft where it goes thru the cutlass bearing because the fouling was threatening to tear the P bracket off. Not a good start 2 the holiday!

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[DavidJ]

"It is likely that if either fuel or air filters started to block up, they would do so in tandem"

Very unlikely, the chances of two filters being subjected to exactly the same situation at exactly the same time is so remote it's not even worth considering. Even with a bad fill of fuel, one tank will probably have more fuel than the other to start, therefore the concentration of good/bad would be different.

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[martynwhiteley]

Mmmm....

Not sure I can fully concede on this one.

I've much more experience looking after filtration systems on process plants than boats, but there must be a similar logic.

Both filters are sited in a similar location drawing the same process fluid (ignoring duel fuel tank aspects which I admit I had not considered).

If a twin engine installation was operated in a very dusty environment, or subjected to dirty fuel (from the same tank), I maintain that it is likely that both filters will deteriorate with a similar dp as time goes on.

Where is the logic that suggests the filters would clogg up at different speeds?

I doubt this is the cause of the problem, but was only pointing out that closing the book' on mechanical factors may be a little premature.

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[DavidJ]

I guess the logic comes from when you have a number of variables at play then the chances of them peaking at the same time are remote. (2 perhaps not 3 and never ever 4)
I find the opposite quite useful when problem solving. When two 'out of the ordinary' things happen (even though they may seem unrelated at the time) they are most likely to be connected and in consequence help to identify the problem.


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[DavidJ]

"How does fouling go in the Med? Does the growth slow down from now on?"
I honestly don't know. My feeling is that there is no let up until the winter.
David


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[oldgit]

Nothing to do with weight I suppose? Maybe water/fuel up to brims and loads of gear/booze/girly junk on board.......Erm please ignore last bit.

<hr width=100% size=1>Two boats please one here n one in the Med

 

[longjohnsilver]

You\'re on!!

But you do need a tank of air on the boat, worth keeping anyway for emergencies. Could show you how to use it, all very simple if only used for going under a few feet and not proper diving.

Hmm, 300 euros for cleaning a hull, maybe I should have a working holiday for a few weeks each year /forums/images/icons/smile.gif

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[DavidJ]

Re: You\'re on!!

You wouldn't get a refill in the Med (and I hope not in the UK) if you didn't have the appropriate diving qualification.
David

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[longjohnsilver]

Re: You\'re on!!

No problem with qualifications, have more than most. Also no problem filling up in the UK without any paperwork, it's not a requirement here and never has been.

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[DavidJ]

Re: You\'re on!!

I guess in the UK there is the assumption that if you own a cylinder then you are probably qualified which must apply to 99.9% of cases.
I did my boat (37ft) last year (BSAC qualified incidently) Mikes 48 footer would take quite a long time but for €300 I'd have a go.

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[EME]

I've always believed that there are 2 reasons why boats are fundamentally slower in the Med than 'Ocean' waters. The first is the SG of the water (salt content). It is saltier /denser therfore allegedly reduces speed by 7-10%. The second is water temperature which does something to the molecules with a similar ( but much, much smaller) effect.

I can not remember , how or why I 'know' these 'facts'. I'm sure the Enginneers out there will collaborate or otherwise.

<hr width=100% size=1><font color=blue>I am WHAT I say I am</font color=blue>

 

[Deleted User YDKXO]

Yeah but the boat reached its design max speed in Mallorca or is the SoF more salty??

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[Deleted User YDKXO]

Certainly, boat is now fully stocked with essentials like booze and cigars but I have regular culls of girly type stuff (SWMBO has'nt twigged this yet which just goes to show how useless girly stuff is) so boat weight has'nt increased that much. Have also tested the boat with tanks full and nearly empty tanks and not huge difference in speed

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[longjohnsilver]

Re: You\'re on!!

BSAC also, 2nd class back in 1982/3, none of this PADI nonsense!! /forums/images/icons/laugh.gif

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