MapisM
Well-Known Member
LOL, wazzat? The equivalent of the neapolitan horn luck?
Around here, not many boaters (including professionals, as fishermen etc.) go at sea without one!
Around here, not many boaters (including professionals, as fishermen etc.) go at sea without one!
rbcoomer
Well-Known Member
thankyou for providing such a thorough explanation which I have digested and learned from.
I am still left with niggles which I will have to live with for now.
Reeds start to move well in front of the hull.
The depth of water in the trent is about 15ft which I wouldnt consider as shallow for my boats.
The water certainly isnt shallow in hurst narrows or the Alderney race either.
I dont ease the throttles back just because I get a tidal push.
My boats appear faster when punching a fast current in that the log is 1-2 knots more at max revs.
Perhaps (but doubtful) my last boat was over propped, but my current boat has an electronic governor which limits revs. so it appears its not just me that is being fooled into thinking its faster against a fast flow but also my instrumentation (paddle wheel log) is also being fooled.
The good news is, it doesnt matter a jot
I'm not an RYS instructor, I dont plan critical passages with tight tolerances so it really doesnt matter if I believe in something that hasnt been scientifically proven (yet).
I also have a 22ct Gold St Christopher at my helm ready to clutch onto
I suspect this is more to do with water density than flow. On a river this will be affected by salinity and perhaps the tidal flows result in temperature fluctuations which also affect density? I'm not a scientist so can't say with any certainty, but increased density could mean less prop slip and thus more bite? Also, a strong current means the water is being 'pushed' or under pressure - does that have an effect on reducing cavitation compared with still water or is it immaterial when compared to the gravitational force already pushing down? (Just to scramble the grey matter a bit more...
)
oceandrive
Well-Known Member
Well we never bother working fuel out. the answer seems to be too scary, and certainly dropping a 100 rpm on a cruise would by dinner for all on board in a good restaurant. But for the maths experts amongst you we have some 480 hours on the engines and I have put 124,000 euros through to tank. so If anybody wants to work out a MPG or a GPM for me it would be appreciated. Ta
D
Deleted User YDKXO
Guest
Say fuel cost averaged €1/litre. Thats equivalent to 57 gals/hour. Say you average overall 15kts, thats about 0.26mpg which sounds about right for a 92 footer
oceandrive
Well-Known Member
Mmmm and thats why we dont work it out!!!!
Powersalt
Well-Known Member
first read this post when away and not signed in to reply, hence my delay. But come on now, we have often tried displacement speeds but in any coastal passage the roll can be awful, plus the added sound of all the crockery rolling around in the cuboards and the table sliding about. Its just not practical on a planning boat or thats my opinion.
Plus what about traveling at circa 1000 revs, wont that polish the engine cylinders and do damage in the long term??
Plus what about traveling at circa 1000 revs, wont that polish the engine cylinders and do damage in the long term??
jfm
Well-Known Member
Haha! Last week I bought the 36000th litre that my boat has taken on this season but I can see i have some way to go to catch up with Mr G
MapisM
Well-Known Member
Blimey, that would be good for 15 thousands NM or so with my boat!
I'm glad I could burn a tad less in all these years, it was nice to have some change left in my pockets to fund the wine reserve...
Hurricane
Well-Known Member
I'm afraid that our electronic displays are only showing about 80,000 litres of fuel but that in three years so it probably doesn't count.
Jeepster
Well-Known Member
Quite the opposite...The slower the revs, the less the engine wear.
Jeepster
Well-Known Member
Well even though my boat has a planing hull I only have a 9.9hp four stroke outboard on it so displacement cruising is unavoidable.
Its only a 450kg displacement 17 footer, and on a flat calm Solent the other day, we were cruising at 6knots (7mph) flat out with six adults on board.
We went from Lee on the Solent to Wooten creek, I.O.W, stayed the night there and then went across into Portsmouth harbour the next day and had a cruise around for a few hours before heading back to Lee on the Solent.
Not sure of the exact distance covered but it was probably around 15 miles total and we used about 10 litres of Petrol. My fuel tank only has 25litres capacity and we roughly used about half a tank.
So I think thats roughly about 5 mpg...I dread to think what it would drop to at planing speeds if we had the 50hp+ outboard I'd like.
Do you think its possible that a bigger outboard at slow revs could be more economical than a small outboard like mine at high revs.
Its only a 450kg displacement 17 footer, and on a flat calm Solent the other day, we were cruising at 6knots (7mph) flat out with six adults on board.
We went from Lee on the Solent to Wooten creek, I.O.W, stayed the night there and then went across into Portsmouth harbour the next day and had a cruise around for a few hours before heading back to Lee on the Solent.
Not sure of the exact distance covered but it was probably around 15 miles total and we used about 10 litres of Petrol. My fuel tank only has 25litres capacity and we roughly used about half a tank.
So I think thats roughly about 5 mpg...I dread to think what it would drop to at planing speeds if we had the 50hp+ outboard I'd like.
Do you think its possible that a bigger outboard at slow revs could be more economical than a small outboard like mine at high revs.
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Kawasaki
Well-Known Member
Well even though my boat has a planing hull I only have a 9.9hp four stroke outboard on it so displacement cruising is unavoidable.
Its only a 450kg displacement 17 footer, and on a flat calm Solent the other day, we were cruising at 6knots (7mph) flat out with six adults on board.
We went from Lee on the Solent to Wooten creek, I.O.W, stayed the night there and then went across into Portsmouth harbour the next day and had a cruise around for a few hours before heading back to Lee on the Solent.
Not sure of the exact distance covered but it was probably around 15 miles total and we used about 10 litres of Petrol. My fuel tank only has 25litres capacity and we roughly used about half a tank.
So I think thats roughly about 5 mpg...I dread to think what it would drop to at planing speeds if we had the 50hp+ outboard I'd like.
Do you think its possible that a bigger outboard at slow revs could be more economical than a small outboard like mine at high revs.
Jeepster
Just looked at your boat piccies
Nice
Hey Man you seem to have fun even with the 9 hp attached!
But what fun you would have with a 50 as you mention
If you are happy trolling along at displacement speeds leave well alone
BUT
Where you are there are times when a 9hp will restrict your progress and ability to go where you want
Obviously you know that and have worked stuff out like tides and all that to do the trip you just did!
Mental note to oneself 'Kwack gerra life'
Anyroad
The boat you have will belt along Lluurverrly with a bigger engine but wont like it at a speed just above 8 knots
But will love it at 16 and above
So fuel consumption will suffer at the 'inbetween speeds' ie above 8 and below 16 ish
Planing hulls like yours do not like to chunter at semi displacement speeds and become rather thirsty
I reckon your boat with an engine that will make it 'Plane' will use about 4 galls an hour at 20kts ish
Pending on make model year etc
But remember
Thats 20 miles in 1 hour
Yer takes yer choice Mate
wild garlic
New Member
Better fuel can help
I have a fairly heavy 27ft motorsailer I use Shell V power keeps the filters clear and there is an increase in power, she does 7.5 knots in most conditions the shell fuel means I dont have to apply so much power when entering or leaving habour thus not taxing the engine
I have a fairly heavy 27ft motorsailer I use Shell V power keeps the filters clear and there is an increase in power, she does 7.5 knots in most conditions the shell fuel means I dont have to apply so much power when entering or leaving habour thus not taxing the engine
D
Deleted User YDKXO
Guest
Rolling is a prob in any boat at d speeds, not only on planing boats but also d and semi d boats but these days both fin and gyro stabilizers are available for all types to deal with that. As for bore glazing, yes that may be an issue, although less so on modern electronically fuelled engines, but 5 mins a day at planing speed should deal with that
Hurricane
Well-Known Member
Not convinced about the roll argument if you pick the weather.
Here's a video that shows a typical "pootle" - no stabilisers.
The other boats in the video are 50 footers.
And - yep - a quick blat at the end keeps the glazing at bay - IMO
colingr
Well-Known Member
So I think thats roughly about 5 mpg...I dread to think what it would drop to at planing speeds if we had the 50hp+ outboard I'd like.
Do you think its possible that a bigger outboard at slow revs could be more economical than a small outboard like mine at high revs.
Well to give you some ideas we're 21ft with a 4.3ltr inboard. aT 25 knots (cruise planing speed) we're burning about 4gph so roughly 6mpg. At full chat of 40knots it's a lot more gph but a lot more fun.
As an example on Saturday we went from Southampton to Yarmouth, back to Osbourne Bay, down to Ryde and back to Southampton, a round trip of a bit over 40Nm on 10 gallons. Mixture of speeds from pottering to 30 knots.
Not sure about displacement as we tend to avoid it once we get out of the river.
I would have thought with a 40 or 50 hp 4 stroke outboard you'd do better than that.
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jfm
Well-Known Member
Mike! That (lovely, thanks!) vid was in a sea that had nowt but little ripples compared with your ~70foot boat. The whole case for stabs is based on bigger seas than that or at least an inability to pick seas as flat as that!
Hurricane
Well-Known Member
Yep - but that was my point - and as you know there are loads of days in the Med when you can do this.
Actually, this was a bit rougher than usual.
BTW - sorry about the music - I think it was Magic FM over the satellite!!!
MapisM
Well-Known Member
LOL, yeah, I guess one could be even more skeptic about roll, if moored in a marina...!
Jokes aside, of course I fully agree that it wouldn't make sense to fit fin stabs on ANY boat, if the assumption is to go at sea only in the glorious sea conditions of your clip.
But believe it or not, I would swear that you could have sensed the stabs effect even in that kind of sea.
Didn't you have a veeery slight and slow roll during that cruise?
I'm talking of something which is even hard to perceive, but becomes apparent when walking longitudinally along the boat walkaround, frinstance.
I think we all experienced that, even in very calm seas (and even on ships!), to the point that we get so used to that to consider it inevitable, as something "embedded" with the boating experience.
But as a matter of fact, it isn't. Not necessarily, at least.
Just try a stabilised boat, where someone else is switching the equipment on/off, while you stay somewhere relatively far from the boat COG - e.g. the flybridge or the walkaround.
Trust me, even in calm seas you'll be able to tell EXACTLY when the stabs work and when they don't, even without looking at the helmsman switching them on/off.
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jfm
Well-Known Member
Yup, exactly correct imho
