Semi displacement / planing, fuel prices

[n.herring]

Yes,maybe chartering first would suit both of us though not certain we would be evaluating the same thing. I already know,after 4 years with a thirsty-at-planing-speeds SD that the sudden fall-off in economy pisses me off.Personally,I would like to know how effective stabilisers are on a SD,particularly at D speeds.I can't think I would ever consider a future SD or D boat without them.However,I still tend to prefer the appeal of D & SD - I agree with BartW and perhaps yourself,there's just something about the solid ship-like feel of some of them which most planing boats don't quite capture. I drool every time I see one of the bigger Selene's,for instance and I love the go-anywhere versality and personality of my current SD.
I assume the Beneteau is the Swift 52. Looks useful and a good size compromise especially for finding mooring slots. The MBM test suggested a high teens cruising speed at around 0.6mpg,suggest that both the speed and economy might drop quite a bit with fouling,though.
Best of luck whichever way you go.

Bought an Aquastar 48 with stabilisers last year, can now go across to Cowes at 6 kts and not worry about the wash from the Red Jet or anything else. Put a cup of tea on the table and it stays there, turn the stabs off and you are all over the place! They are brilliant.
Hope to get at least 2mpg at up to 7-8kts, gets painful at 25 kts though probably nearer 0.7mpg.
Hope to do a lot more gentle cruising this year, enjoying the journey rather than rushing everywhere. Neil

 

[Deleted User YDKXO]

Yes,maybe chartering first would suit both of us though not certain we would be evaluating the same thing. I already know,after 4 years with a thirsty-at-planing-speeds SD that the sudden fall-off in economy pisses me off.Personally,I would like to know how effective stabilisers are on a SD,particularly at D speeds.I can't think I would ever consider a future SD or D boat without them.

Maybe send a PM to piers of this parish. He has a Fleming 55 which I think has stabs and I believe he uses it mainly at D speeds

 

[stillwaters]

Bought an Aquastar 48 with stabilisers last year, can now go across to Cowes at 6 kts and not worry about the wash from the Red Jet or anything else. Put a cup of tea on the table and it stays there, turn the stabs off and you are all over the place! They are brilliant.
Hope to get at least 2mpg at up to 7-8kts, gets painful at 25 kts though probably nearer 0.7mpg.
Hope to do a lot more gentle cruising this year, enjoying the journey rather than rushing everywhere. Neil

Thanks for the info. Know what you mean about enjoying the journey,especially as this keeps the wife onside.
What type of stabs have you got and are they also any good at anchor?

 

[jfm]

The 50ft v 40ft thing: I would think the P50 will feel 50% bigger rather than the 25% suggested by the difference in length because it's higher, wider and heavier as well as just longer. I suspect that the difference between 14tons and 24 is probably going to be a better indication of the difference in how they feel than the difference between 40 and 50 feet.

I'd agree that bjb. I sensed a huge difference, x2 perceptionwise, in going from 42 to 58. There were many common sea states where a 42 is a bit scary and a 58 just chomps through. I would therefore expect significant step up feeling from 42 to 50

Ref the Bene52 trwler, I've always liked it. A colleague here in the office wanted one and priced it up, and was amazed by the prices for essential options. 25k for a passerelle kinda thing. Once you have specced it well any initial attractiveness to the price is long gone. Also I've heard rumours it will be replaced soon by a approx 55 with pod drives

 

[stillwaters]

Maybe send a PM to piers of this parish. He has a Fleming 55 which I think has stabs and I believe he uses it mainly at D speeds

Thanks,I mentioned Piers and his F55 earlier in this thread as I believe he may have said something about having to go at planing speed for his stabs to be effective,though he prefers 8kn when possible.Not certain if I'm right,though.
I think the post from n.herring about having an Aquastar 48 with stabs working well at 6kn is promising,especially if they turn out to be of the less exotic variety and are good just because of their being the recently improved technology that they all now seem to have. Might be of use to yourself.

 

[jfm]

for me planing boats with stabs is the way to go,

the one thing that I like about SD boats is:

I've alway's been a fan of trawler boat models, and these are usually SD.
but thats just taste,
they appear to me like real "ships" and thats what I like,
nothing to do with D-SD-P
nothing to do with efficiency, ...

I'm not (yet) convinced that there is much difference in behaviour (in bad sea state) between the 3 types. After all they are just a floating piece of GRP or wood in a huge sea,
and for the limited "holiday" time I spend on her,..a planing boat offers just that bit more enjoyment.
I prefer to stay ashore when the sea state doesn't allow a pleasant cruise,

I'm not planning any ocean crossing, nor any canals cruising (where D boats make sense)

My planing boat is quite heavy,
when the sea state is bad, I can cruise at a SD speed which could make the ride more comfortable (in some conditions).

Agreed 100% Bart!
Even without stabs what you say makes good sense for henry imho

 

[Deleted User YDKXO]

Ref the Bene52 trwler, I've always liked it. A colleague here in the office wanted one and priced it up, and was amazed by the prices for essential options. 25k for a passerelle kinda thing. Once you have specced it well any initial attractiveness to the price is long gone. Also I've heard rumours it will be replaced soon by a approx 55 with pod drives

Yeah you're right. If you can live with a poverty spec, its a £650k boat but add a few essential extras and its pushing £800k and thats getting into more rarified territory

 

[n.herring]

Thanks for the info. Know what you mean about enjoying the journey,especially as this keeps the wife onside.
What type of stabs have you got and are they also any good at anchor?

The stabs are Wesmar, fin type. The ones I have do not work at anchor but are excellent when underway. Certainly not the exotic variety but very effective none the less . Besides being good at slow speeds they are also very effective and make a difference in the rough at higher speeds, goes from wish I wasn't here to being acceptable. N

 

[stillwaters]

The stabs are Wesmar, fin type. The ones I have do not work at anchor but are excellent when underway. Certainly not the exotic variety but very effective none the less . Besides being good at slow speeds they are also very effective and make a difference in the rough at higher speeds, goes from wish I wasn't here to being acceptable. N

Thanks for that,I'm sure they are exotic enough for most of us,working at 6kn and over certainly takes care of most of it. I think Wesmar were maybe the first to use electronic rather than hydraulic controls and,consequently, were main suppliers to US forces so must know what they're about,presumably.

 

[Nautical]

Yup true, most SD boats' fast cruise is in the teens although you can shoehorn enough power into some of them to hit the mid '20's kts whereas most planing boats will easily cruise in the mid 20's kts. Speaking for myself, my next boat will probably be a SD boat but I'm going to do a couple of charters on SD boats first before I buy anything because I'm really not sure whether the slow cruising speed and higher fuel consumption of a SD boat will piss me off. Maybe a charter first is the way to go for you before you buy?
Just going off on a tangent a bit, I like what Beneteau have done with their range of Fast Trawlers which seem to offer a little bit of the best of both worlds. Seaworthy hulls which are supposed to be good at both SD and D speeds but capable of 20kt+ cruising and importantly with fuel consumption that seems comparable to a planing boat. Of course, the Beneteau finish is not upto the standard of some other builders

You could try a charter on one of the these

http://www.outerreefyachts.com/index.cfm?p=news/article_photos&x=82&h=01

recently delivered and working out of Cairns to the Barrier Reef, you can go by sea plane and meet her out on the Reef and carry on from there. So far everyone has had an absolute blast, said was the best they have every been on, part I am sure to the skipper who is typical laid back Aussie and the tons of toys, fishing and dive gear aboard.

Sorry for the plug, but I don't know of any other 70' SD charters, does anyone?, be interested to know

 

[henryf]

I looked at the Trawler 52 and it does indeed look interesting on paper. I'm not sure about the ship lap tongue and groove on the side, they must have been passing Wickes as they were finishing it off.

I couldn't find any for sale in the UK and they are all just a bit too much for me. Not sure how many will actually sell. You need wait until a dealer gets hold of one as a stock boat then you'll find out what they are really worth.

I think we might have been on one a few years ago at Southampton but I must have visited late on in the day after a couple drinks because I can't remember it other than the missus moaning about the tongue & groove cladding on the outside.

Anyway Portsmouth harbour looking nice and peaceful and a load of ships waiting offshore at the Nab tower. Southampton and the Isle of wight look glistening in the distance from the other side. Having a crash pad on the 11th floor comes with a few perks

Henry

 

[Piers]

I mentioned Piers and his F55 earlier in this thread as I believe he may have said something about having to go at planing speed for his stabs to be effective,though he prefers 8kn when possible. Not certain if I'm right,though.

Hi stillwaters,

The stabs are just as effective at all speeds. The speed input (auto or manual) automatically adjusts the amount of deflection. So no need to worry about your cruise speed.

We cruise at approx 8kts, and the stabs are brilliant. Evn in flat waters, my wife knows within a few moments if I tuen them off !

The fun thing to do is whilst moored alongside a pontton, is to enter a speed manually and the rock the boat. The winglets throw water all over the place!

Mine are Trac in case I hadn't mentioned that before.

 

[Piers]

Higher speed with stabs with planing hulls

Another interesting bit of info is that on planing boats, stabs are shown to increase top speed, not reduce it.

I've been told by one (major) UK builder, that contrary to the thought that the stabs would add drag and therefore reduce top speed, the opposite happens.

By stopping the boat rolling, there is less wetted area of the hull, therefore less drag, therefore a higher top speed.

 

[jfm]

Another interesting bit of info is that on planing boats, stabs are shown to increase top speed, not reduce it.

I've been told by one (major) UK builder, that contrary to the thought that the stabs would add drag and therefore reduce top speed, the opposite happens.

By stopping the boat rolling, there is less wetted area of the hull, therefore less drag, therefore a higher top speed.

I've heard that one too Piers. It's one of those stories oft-repeated by some sales types or boatbuilder staff who have a loose grasp of engineering. AKA bollox! Fin stabs cost about a knot in top speed and add a litre per mile at cruise speed.

 

[stillwaters]

Hi stillwaters,

The stabs are just as effective at all speeds. The speed input (auto or manual) automatically adjusts the amount of deflection. So no need to worry about your cruise speed.

We cruise at approx 8kts, and the stabs are brilliant. Evn in flat waters, my wife knows within a few moments if I tuen them off !

The fun thing to do is whilst moored alongside a pontton, is to enter a speed manually and the rock the boat. The winglets throw water all over the place!

Mine are Trac in case I hadn't mentioned that before.

Thanks Piers,that's good to hear and I can understand why your wife appreciates them. Certainly for me,the difference in comfort in the choppy rough stuff could well be the deal-breaker with my wife. I've heard that TRAC are very good,am I right in assuming from what you say that yours are the at-rest Tracstars,which I believe have been around for a while now?

 

[Deleted User YDKXO]

You could try a charter on one of the these

http://www.outerreefyachts.com/index.cfm?p=news/article_photos&x=82&h=01

Fully aware of that one, Trev! Anything a bit closer to home and in the 58/63 size?

 

[Nautical]

Fully aware of that one, Trev! Anything a bit closer to home and in the 58/63 size?

Not yet but a new 63 with a Ken Freivokh interior on its way which may be in the charter market later this season, keep you posted.

I have tried to find a SD trawler style charter around the EU for ages but can't find anything, lots of old coverted fishy boats and much older stuff but nothing modern.

 

[jfm]

...Trawler 52 ... ship lap tongue and groove on the side, they must have been passing Wickes as they were finishing it off.

The clapperboard is actually a (very high, like everything else) cost option Henry so you can just have it without if you prefer. Hull #1, the one in the brochure, called Phileas, is parked round the corner from me (all the brochure pics are Lerins islands round the corner from Antibes) and they have let the teak go all silver grey so it looks like manky old potting shed. If people spec this teak they should at least oil it!

 

[stillwaters]

I've heard that one too Piers. It's one of those stories oft-repeated by some sales types or boatbuilder staff who have a loose grasp of engineering. AKA bollox! Fin stabs cost about a knot in top speed and add a litre per mile at cruise speed.

By the way,thanks for your earlier input on my stabs question.
I too have also been rather sceptical about the various manufacturers' claims about greater economy resulting from fitting stabs and,by the sound of it,you have obviously found the opposite to be the case. However,consider this. Are your figures based solely on planing boats as opposed to semi or maybe even disp ones,cos I think it might possibly have some bearing on where these salesmen claims could have originally took root. The thing about P boats is,of course,that they are designed to be flyers,not quite literally but more in the sense of their lifting on to the top of the water thereby with less hull in the water and therefore less drag than SD or D boats. It isn't necessarily extra weight that makes SD or D have lower speeds,it's mainly due to the increased hull in the water generating greater drag that slows them down. Most similar size boats,no matter what hull shape,in D mode tend to have fairly similar fuel economy because at D speed they're generating far more similar levels of drag. However,an SD in P mode typically produces about 2/3 the speed and 2/3 the fuel economy for this lower speed of its P equivalent. Easy to prove if you look at say a typical 40ft P & SD,both of similar weight ie.displacement at zero speed. They'll produce similar stats up to 8-9kn then from there on the SD will fall away quite rapidly. Obviously because even once planing,the SD will have more hull still in the water than the P boat.
Consequently,at P speed your lean & mean P boat has comparatively less drag than an equiv SD,therefore the additional drag of fins will have far more effect on speed and economy than an already inefficient high-drag SD where the relatively small extra drag will be offset by the better directional stability provided by the stabs. That's the other thing about SD & D hulls for that matter,in anything beyond flat water they do tend to waste quite a bit of forward momentum due to roll and the deviation that results from this. I certainly reckon my SD would travel a shorter distance A to B in broken sea if it didn't roll so much.

 

[Deleted User YDKXO]

. That's the other thing about SD & D hulls for that matter,in anything beyond flat water they do tend to waste quite a bit of forward momentum due to roll and the deviation that results from this. I certainly reckon my SD would travel a shorter distance A to B in broken sea if it didn't roll so much.

Thats an interesting idea. Planing boats have a very high degree of hydrodynamic stability at planing speed due to the flat surfaces aft designed to give the hull lift so they roll less in a beam sea and maintain an optimum attitude which minimises hydrodynamic drag. SD boats on the other hand develop less lift and less hydrodynamic stability which means that they roll more at planing speed and because of that, hydrodynamic drag is increased as the optimum attitude of the hull cannot be maintained. Hence stabilizers help to increase speed in a SD by maintaining a more level planing attitude? Is this the theory?