rustybarge
Well-Known Member
We're all members of the Bullingdon Club; we discuss an eclectic and diverse range of interesting subjects.
View attachment 36773
Bolt on Surface Drives/ Rudder.
- Thread starter rustybarge
- Start date
We're all members of the Bullingdon Club; we discuss an eclectic and diverse range of interesting subjects.
View attachment 36773
Latestarter1
Well-Known Member
Yes but including outdrives is simply perverse not diverse.
rustybarge
Well-Known Member
aah yes, but the surface drive IS an outdrive, because it's located outside the hull!
I was thinking if it didn't work out as a surface drive, just drop it a couple of feet and you have a conventional shaft drive.
Last edited:
MapisM
Well-Known Member
LOL, maybe because you must be the one and only folk on the planet who actually heard of an LM surface drive installation...?
MapisM
Well-Known Member
That's also true for the outdrives which you should consider in a comparison with surface transmission.
It doesn't make any sense to compare a surface transmission with non-surface outdrives like Merc Alpha/Bravo, Volvo DP, etc.
Not true, I'm afraid. I've seen various boats equipped with surface transmissions (alas, none with this LM thing), and in all of them, bar none, the shafts were below the w/l.
rustybarge
Well-Known Member
rustybarge
Well-Known Member
In all fairness, it looks like a neat 'drop into place' unit with fitted rudder.
I could cut out the center plate between the alloy pods on the cat, and bolt the surface drive unit into place.
The shaft could then go through the deck, maybe 2'-3' into the cockpit and hook up to the engine/gearbox.
It would be easy to weld up a cradle for the engine, bolting it to the transom.
View attachment 36775
a yanmar 110 hp diesel looks good at 250kg inc gearbox.
Maybe v-drive gearbox...?
I could cut out the center plate between the alloy pods on the cat, and bolt the surface drive unit into place.
The shaft could then go through the deck, maybe 2'-3' into the cockpit and hook up to the engine/gearbox.
It would be easy to weld up a cradle for the engine, bolting it to the transom.
View attachment 36775
a yanmar 110 hp diesel looks good at 250kg inc gearbox.
Maybe v-drive gearbox...?
omega2
Well-Known Member
If you are considering a V drive then why bother with a surface drive?
MapisM
Well-Known Member
WTF?!? I can't read your attachment, but neither an outdrive nor a surface transmission can be specced for an installation half an inch (or whatever) "above the w/l".
And if LM does, I wouldn't trust them as a hamburger supplier, let alone for a marine transmission...!
They can (and should!) specify the so called "X dimension", which is the distance between the keel bottom and the shaft, but that has nothing to see with the w/l.
The w/l not only depends on the hull, but it can vary even with the same hull, for instance because available with different engines.
PS: re. what you're thinking to do with your cat, I'd suggest to consider the first answer which you got in this thread. It says it all, really.
Last edited:
rustybarge
Well-Known Member
All the weight on a cat is biased towards the back, so the engine would have to be pushed as close to the transom as possible. An ordinary shaft drive setup runs with the propellor deeply submerged, so the engine would have to be located in one of the hulls to get the correct shaft inclination.
250kg sitting in one side of the boat would heel it over to one side, and upset the lateral balance.
rustybarge
Well-Known Member
As a guide exactly half the prop is submerged. As you can see from the drawings the shaft enters the transom above that point.
View attachment 36776
But what happens in a choppy sea.....a prop on the surface must be out of the water for a considerable amount of the time?
Last edited:
MapisM
Well-Known Member
LOL, hang on, that's NOT the hull waterline!!!
The drawing shows how a surface drive works AT SPEED - i.e. with the hull fully planing.
That tells us just about nothing re. the actual hull w/l, which you can check only with the hull at rest (or at low D speed), and anyhow is bound to be MUCH higher than that (I mean, with the hull sitting much lower in the water).
And re. your last question, yes, that's definitely another problem of surface transmissions.
Or better said, it's one of their characteristics - remember, they are made for speed, not for seakeeping.
You'll never see them in a lifeboat...
Divemaster1
Well-Known Member
Yup it happens ... and if you're running hard like this (from RB 2008 when we were a safety boat)..., you then need to consider the water intake .....
Just for the record, it is not really worth considering surface drives unless you'll head for 20 knots plus.... and usually much more than that..... Those exposed cleaver props will set you back some serious ££ and don't take kindly to debris in the water....
rustybarge
Well-Known Member
Yup it happens ... and if you're running hard like this (from RB 2008 when we were a safety boat)..., you then need to consider the water intake .....
Just for the record, it is not really worth considering surface drives unless you'll head for 20 knots plus.... and usually much more than that..... Those exposed cleaver props will set you back some serious ££ and don't take kindly to debris in the water....
Is it an Aeroplane or a boat......?
vas
Well-Known Member
I think they're boats filled with air, so aeroboats, no?
RB, 25-30knt is where the surface drives start "working"
further you basically have no steering at low speeds and iffy dodgy one at higher speeds. A guy I know with an Aermar 36 (Italcraft, beautiful boats imho) used to steer with the trim tabs
You are going to go for two engines on your cat, arent you?
cheers
V.
rustybarge
Well-Known Member
I think they're boats filled with air, so aeroboats, no?
RB, 25-30knt is where the surface drives start "working"
further you basically have no steering at low speeds and iffy dodgy one at higher speeds. A guy I know with an Aermar 36 (Italcraft, beautiful boats imho) used to steer with the trim tabs
You are going to go for two engines on your cat, arent you?
cheers
V.
After due consideration, I'm shelving the surface drives.
Jets are the answer, no not water jets...the other sort.
rustybarge
Well-Known Member
I think they're boats filled with air, so aeroboats, no?
RB, 25-30knt is where the surface drives start "working"
further you basically have no steering at low speeds and iffy dodgy one at higher speeds. A guy I know with an Aermar 36 (Italcraft, beautiful boats imho) used to steer with the trim tabs
You are going to go for two engines on your cat, arent you?
cheers
V.
Sorry didn't notice your question.
I've taken early retirement on a modest pension, so The criteria for my boat project had just two requirements: Economy and the abilty to make reasonably long coastal trips in all weather conditions, obviously within reason in a very small boat.
With one 90hp Suzuki leanburn, ( 20% saving over twins) the cat should cruise at 18kts/3gl.hr/4000revs.......6mpg!
...I'll bring along a standby OB as well.
So far the project is making good but slow progress due to hold ups over suitable materials, the lastest solution is aluminium sandwich panels with 3mm polythene center for the hardtop roof (€38 4' b y8') Just delivered on Monday, will be fitting over the next few days...weather permitting.
Latestarter1
Well-Known Member
LOL, maybe because you must be the one and only folk on the planet who actually heard of an LM surface drive installation...?
Only because a well respected powerboat racing friend endorsed them. Whilst I realise that subject is now closed just had this product pop up, to be launched by Michigan Wheel at Seawork 2014 http://www.seafury.com/a/Home
It would appear that these modified surface drives as opposed to pure racing Arnson drives and their clones, these units with separate rudders may have some merit. Certainly on the list to visit when at Seawork.
rustybarge
Well-Known Member
From an engineering prospective, I love the concept, it's so simple and maintenance free. Just a couple of cutlass bearings.
.....and the real test: commercial operators use the design.
Because the prop's work on the surface a couple of foot higher that a conventional shaft drive, it suits a Cat design perfectly. On a single engine installation the prop shaft can be centrally located between the hulls, and the shaft led back and through the wing deck to a vee-drive gearbox....locating the diesel close to the transom.
Please be the first to try it out...........
. View attachment 36824Ps: crazy idea. Buy a surface drive prop and try it on an outboard motor raised vertically on a small frame, to see if it works!
Last edited:
rustybarge
Well-Known Member
Being a bit of a cynic, maybe it would be a good idea to try out a mini-surface drive system like they use in Thailand, called a Long tail.
This one's designed for a small 20 hp stationary air cooled engine, like a Honda etc.
Anyone interested in trying one out?
It comes as a kit of parts....you supply the engine yourself.
Video:http://www.mud-skipper.com/the-longtail-or-mud-motor-kits.html
Kits:http://www.mud-skipper.com/the-longtail-or-mud-motor-kits/16-23-hp-longtail-motor-drive-system.html
View attachment 36833
This one's designed for a small 20 hp stationary air cooled engine, like a Honda etc.
Anyone interested in trying one out?
It comes as a kit of parts....you supply the engine yourself.
Video:http://www.mud-skipper.com/the-longtail-or-mud-motor-kits.html
Kits:http://www.mud-skipper.com/the-longtail-or-mud-motor-kits/16-23-hp-longtail-motor-drive-system.html
View attachment 36833
Last edited: