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Old 22-09-2019, 18:52   #1
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Long tail on a small catamaran (30-36' or so)

Inboards are a nuisance, and outboards are not great either. I do not like dragging metal through salt water when it is not being used, I don't like through hulls, I don't like tiny cramped engine compartments..........I have a number of gripes about outboards too, but one significant factor is that it is a single purpose engine...... it is nice to be able to lift them off the boat easily, but they have pathetically small charging capacity, and no utility for any other function than propulsion.
A small diesel can drive the boat generate significant electricity if needed, it could operate a high pressure pump for a watermaker or cleaning the hull... A watermaker pump after all is just a pressure washer pump... It could drive a hooka...... the possibilities are only limited by the imagination.

I'm envisioning a small diesel engine on a tilting frame with a solid bottom to keep splash from reaching it, and sides that tilt down with it. The shaft runs aft, and is lowered into the water for propulsion when needed like a longtail. A pair of rudders would drop with it, serving to vector the thrust for steering. The whole shaft assy would be up against the bottom side of the deck when lifted. On a boat of that size, the engine might need to be forward of the cabin to keep the angles reasonable.... engine lubrication, etc.



A mad idea perhaps..........but I don't see a lot of reason why it wouldn't work.
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Old 22-09-2019, 22:37   #2
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Re: Long tail on a small catamaran (30-36' or so)

A few years ago I saw some pictures of a Wharram Tiki-38 with that same idea of long-tail-style engine power. Hopefully that is enough info to google it.
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Old 22-09-2019, 23:41   #3
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Re: Long tail on a small catamaran (30-36' or so)

Would need to be an engine and gearbox on a movable frame. Heavy, unless you got the balance right. How would you propose to cool it?
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Old 23-09-2019, 00:59   #4
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Re: Long tail on a small catamaran (30-36' or so)

Seems the steering setup would be needlessly complicated. Why not just steer with the rudders you'd use for everything else?

I was thinking about this for a while myself. I had Mercedes straight 6 engine around. Cooling could be just as any automotive engine. A radiator out where there is some wind flow.

The issue is one of complexity and weight.

The whole setup becomes very heavy as compared to retractable outboards. I designed my outboards to be primarily in a position completely clear of the water unless they are being used. You lower them to the water only when motoring. If I am motoring with one, I lift the other out of the water. 4 years in now and they still don't need new zincs.

The diesel does have a lot of advantages as you mentioned, however in terms of cost, weight and time spent working on the boat, off the shelf solutions are, unfortunately, far more efficient.

PS: we think alike. I have absolutely no thru hulls below the waterline. None. The biggest secret to all of this is to try to adapt all of your engineering ideas to making use of off the shelf, non marine and air cooled items. This is the way to achieve no thru hulls, better performance from reduced weight and less cost and greater simplicity.
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Old 23-09-2019, 01:43   #5
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Re: Long tail on a small catamaran (30-36' or so)

Sounds complex, how much drag do you think a folding or feathering prop has?

You are almost at a point of describing a hybrid electric system were the generator can be mounted anywhere in the yacht and used for multiple purposes.

Thought this was interesting:

http://www.hybrid-marine.co.uk/resou...eport-rev3.pdf
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Old 23-09-2019, 02:45   #6
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Re: Long tail on a small catamaran (30-36' or so)

Everything old is new again
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Old 23-09-2019, 05:30   #7
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Re: Long tail on a small catamaran (30-36' or so)

Quote:
Originally Posted by Chotu View Post
The issue is one of complexity and weight.

The whole setup becomes very heavy as compared to retractable outboards. I designed my outboards to be primarily in a position completely clear of the water unless they are being used. You lower them to the water only when motoring. If I am motoring with one, I lift the other out of the water. 4 years in now and they still don't need new zincs.

The diesel does have a lot of advantages as you mentioned, however in terms of cost, weight and time spent working on the boat, off the shelf solutions are, unfortunately, far more efficient.
I think that this mostly sums it up.

@owly, I'm sure you are aware that multiple Wharrams of different sizes have similar setups.

I agree that it would be nice to have a multipurpose engine onboard, for propulsion, charging, and genset/pto uses but again in practice it becomes less so.

So I like the idea in theory, less so in practice. Some minuses:

- poor maneuverability
- no redundancy

Some of that is partially solved on larger Wharrams with twin long tails, or twin drives, often hydraulic, and often with a single engine.

However this has now made the simple idea somewhat complicated again, and if a single engine, no redundancy.

I think the issue of charging is becoming less of a problem now that the way forward is electric and solar, especially so on a catamaran where you can easily mount enough panels (and use them as a permanent bimini).

Also, the issue of fuel should be considered. If a diesel engine, will you also carry petrol for the dinghy outboard? Or will this be electric?

I think that the the twin outboard solution + solar + honda genset for backup answers a lot of these problems with an off the shelf solution, without undue complexity, with lightweight, with redundancy (and what I would call 'modularity' - the ability for 1 part of the package to be interchanged without undue issues), with 1 fuel only required, and with simplicity at least as far as the overall package is concerned for a smaller boat.

On a larger boat, twin multipurpose engines and twin longtails may swing the balance (a Pahi 52 has this setup).

But if you are happy to give up the maneuverability and redundancy of a twin setup, then a combination single engine, long tail, pto alternator, pto watermaker, pto fridge compressor, etc, could be the lightest and simplest and cheapest solution.

I actually had a dc genset on a monohull in the past that did most of this - charging, watermaker pto, dive compressor pto, hot water (via cooling or electric) and I very liked it. If designed from scratch it could have been the propulsion engine too.

As I said, I like the idea (mainly of 'less stuff onboard' in general) but I'm not sure in practice:

- If long distance cruising & staying at anchor the maneuverability is less important.
- But also if long distance cruising the redundancy is very important.


If you need links to Wharrams with these various setups let me know.

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Old 23-09-2019, 07:49   #8
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Re: Long tail on a small catamaran (30-36' or so)

Quote:
Originally Posted by jmh2002 View Post
I think that this mostly sums it up.

@owly, I'm sure you are aware that multiple Wharrams of different sizes have similar setups.

I agree that it would be nice to have a multipurpose engine onboard, for propulsion, charging, and genset/pto uses but again in practice it becomes less so.

So I like the idea in theory, less so in practice. Some minuses:

- poor maneuverability
- no redundancy

Some of that is partially solved on larger Wharrams with twin long tails, or twin drives, often hydraulic, and often with a single engine.

However this has now made the simple idea somewhat complicated again, and if a single engine, no redundancy.

I think the issue of charging is becoming less of a problem now that the way forward is electric and solar, especially so on a catamaran where you can easily mount enough panels (and use them as a permanent bimini).

Also, the issue of fuel should be considered. If a diesel engine, will you also carry petrol for the dinghy outboard? Or will this be electric?

I think that the the twin outboard solution + solar + honda genset for backup answers a lot of these problems with an off the shelf solution, without undue complexity, with lightweight, with redundancy (and what I would call 'modularity' - the ability for 1 part of the package to be interchanged without undue issues), with 1 fuel only required, and with simplicity at least as far as the overall package is concerned for a smaller boat.

On a larger boat, twin multipurpose engines and twin longtails may swing the balance (a Pahi 52 has this setup).

But if you are happy to give up the maneuverability and redundancy of a twin setup, then a combination single engine, long tail, pto alternator, pto watermaker, pto fridge compressor, etc, could be the lightest and simplest and cheapest solution.

I actually had a dc genset on a monohull in the past that did most of this - charging, watermaker pto, dive compressor pto, hot water (via cooling or electric) and I very liked it. If designed from scratch it could have been the propulsion engine too.

As I said, I like the idea (mainly of 'less stuff onboard' in general) but I'm not sure in practice:

- If long distance cruising & staying at anchor the maneuverability is less important.
- But also if long distance cruising the redundancy is very important.


If you need links to Wharrams with these various setups let me know.


I had not been aware that Wharrams had been built with this setup. The ideal engine for that kind of use really would be an air cooled diesel like a small deutz..It would be nice to do away with the use of seawater in any form for cooling, and of course an engine in the foredeck could even have a radiator. There is the advantage of being able to use automotive or industrial engines, but I'm partial to the Yanmars, and the gearboxes are already engineered for the job. Tilt angle of the engine itself could be reduced by shaft length, and possibly a CV joint allowing the shaft to be non-straight without a bunch of power loss.
Propulsion redundancy is not a huge issue, and diesels are extremely reliable. This is a sailboat after all, not a motor boat. An outboard for a dinghy could be a bit over powered perhaps (hard dinghy), and could be used in a pinch for manouvering, perhaps even dropped down forward to act as a bow thruster.
The main redundancy issue really is watermaker dependence. I consider a watermaker a non negotiable necessity these days considering the quality concerns, and availability concerns when voyaging.......... do you really want to be taking public water in a remote pacific atoll where there is a shortage of quality potable water? Not to mention.... have you ever looked in side a cistern ;-).
Weight is mitigated by the lower fuel consumption, and lack of the need to carry large quantities of water. And of course the reduction in battery weight to run a watermaker. Of course regular use ensures dependability in my experience.


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Old 23-09-2019, 07:59   #9
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Re: Long tail on a small catamaran (30-36' or so)

Consider the design of WWII diesel submarines. Fixed diesels running electric motors and charging batteries. I don't know whether the loss is greater in going hydraulic versus transferring the energy by electricity. I do think that a lot of us, faced by prop alignment, engine positioning, charging of the batteries, etc. have dreamed about a fixed engine sitting at the cg, feeding everything (pumps, too) from that location. I suspect that energy loss and extra expense (powerful hydraulic or electric motors) have defeated us all.
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Old 23-09-2019, 09:09   #10
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Re: Long tail on a small catamaran (30-36' or so)

Quote:
Originally Posted by owly View Post
I had not been aware that Wharrams had been built with this setup.
Some examples:

And PS: Wharram builder Seacape Asia often uses variations on your theme. Contact Gunther for info: https://seascape-asia.com/

Customised Wharram TIki 30 with "inboard diesel engine driving a hydraulic pump and motor, turning a single screw. "
https://phuket.boatshed.com/seascape...at-253027.html



Wharram Tiki 38 with "a single Yanmar diesel, driving two hydraulic pumps, motors and retractable props on shafts."
https://phuket.boatshed.com/wharram_...at-247510.html

Wharram Pahi 42 with "Yanmar 3 GM30F and Retractable longshaft ( no Prop in water while sailing) + bow thruster for maneuvering.
https://fenuavoyage.wordpress.com/?f...A8Q_f1w1ohcwuc (admin of Wharram Catamaran facebook group)

recent post: https://www.facebook.com/groups/1104...1782404556289/





Wharram Tiki 46 Wakataitea with "Beta Marine Kubota"
search google, lots of info: https://www.google.com/search?newwin...4dUDCAs&uact=5
Blog: The WakaNahannis at Sea
These cruisers are here under user name NahanniV. They recently broke something on their longtail setup:
Help me re-engineer my Catamaran lifting drive leg

Wharram Pahi 52/53 with "Nutt twin diesel drive system allowing real engine power for a Wharram catamaran: dependable operation in rough seas, superb manoeuvrability & props that retract out of the water when sailing! Up to 1500Nm range under single engine operation @ 5 kts!!!"
Pahi 52 for sale E. Med (ref 1245) - Scott Brown Multihulls

There are more, but that should get you going. Hope it helps
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Old 23-09-2019, 09:22   #11
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Re: Long tail on a small catamaran (30-36' or so)

Quote:
Originally Posted by jmh2002 View Post
.........
If you need links to Wharrams with these various setups let me know.

I'd be interested to see them.
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Old 23-09-2019, 09:30   #12
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Re: Long tail on a small catamaran (30-36' or so)

For all its worth it, I got to drive a true longtail in Thailand and was surprised by how difficult it is. The forces at play are very high and it takes all the strength that you can muster to keep the longtail under control. Granted, those are very primitive setups, but I would guess that getting something similar in principle (but possibly even longer longtail if the engine is forward) to work smoothly would require quite a lot of engineering and quite some tinkering with the design.
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Old 23-09-2019, 09:44   #13
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Re: Long tail on a small catamaran (30-36' or so)

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I'd be interested to see them.
Your boat is linked in my list

But some others are there too.
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Old 23-09-2019, 10:58   #14
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Re: Long tail on a small catamaran (30-36' or so)

Owly, had a “CV” set up before. Big arse motor to an outdrive Merc. One of the happier days in my life when I sold her. In the four years I owned her I had to replace the CV joints twice. Any salt water that enters through the boot ... will eventually seize up the joint

JMH thanks for posting up the Wharram pics. I was astonished at the engineering of dragging that underwater to hold the long tail. Noticed that one guy had broken his set up and asking for advice how to re-engineer it. Da?

I have a trimaran with a 10 hp Tohatsu. If there is any wind sails are up. I can get close to 7 knots on flat water. Keep it simple. Water maker and a a small portable gen work well. Can adapt the high pressure pump to use for spraying down the boat.

Keep it simple and modular. Cheap is good. I haven’t spent over 40 dollars on my outboard in the last 2 years. Change oil, drive fluid, new in line filter, and plug. She sat for 8 months and started second pull. Can’t beat that
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Old 23-09-2019, 11:04   #15
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Re: Long tail on a small catamaran (30-36' or so)

For me this was the simplest way. I can pull and tilt the engine nearly horizontal as high as the beam. What I like about it is that the engine wonít get drowned,it takes up no deck space and itís easy up and down
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