outboard power on larger cruising cats

thanks for the info raf.
design wise I am more inclined to go with a frame that locks into 2 positions
the basic position places the anti-cavitation plate 15 cm below its design level to handle the rough chop better
the harbor/flat sea position sets the plate at its design level for max efficiency.

 

You can check out Pooderbuilt transom brackets, 24 inches of travel, hydraulically operated, normally used for auxiliary motors on power boats, The product is called a power lift.

 

Steve,
I meant the saloon/cockpit bulkhead. They were actually under the cockpit seat, right against the bulkhead.
I had access to them from the top and from the side by removing an aluminium bolted door in the aft cabins.

One motor if going for long trips at slow speed, 5h at the time.
Both when manoeuvring or needed speed.

 

Big mistake..... I think it was price and availability at the time.
Nothing better than those high trust 5 stroke Yamaha

 

Thanks Stefano,
That makes more sense although as I said, a lot of Tennants open bridgedeck cats do have the motor further forward.
When you replaced the Yamahas was it because they were worn out or some other reason? If they were worn out I'm wondering what sort of hours you got out of them. I really have no idea what sort of hours to expect out of outboards. The 25hp high thrust motors we get in the US unfortunately only have a 20" shaft but ive seen others in other countries claim 25" so maybe different countries get different specs.

Steve.

 

No Steve, they were still running as new, no noise or vibrations, like I always says those Yammy 4 strokes are just the best!
My partner in the charter business was operating out of Broome for 6 months, I was operating her out of Perth the other six months.
He sometimes was stuck with no or opposing wind on his way back home and needed to arrive before sunset so he wanted bigger engines. I now remember why we didn't put 60HP Yammy, they wouldn't fit in the nacelles that were designed for 25HP....
So we got those Johnsons. While top speed in flat seas improved, cavitation in choppy seas and no reverse trust were a real nuisance.

And yes, the 25s were XXL, which if I remember correctly are 25" long.
On the dinghy we had a third 25 4strokes,but it was an L with standard high-speed gearbox.

 

You might want to add some cup to that prop. I run a micro drafting boat which wont even get on plane without special props. Add cup and now my prop runs above water level, fed by a tunnel. Reverse does not improve though.

 

Dual Props

What about dual props, ....any outboards using those??

I did find this https://www.youtube.com/watch?v=chfDSJ2d_a4

and this https://www.youtube.com/watch?v=TdcWQpN8hl4

I had suggested dual props here to keep prop dia down in overall size (silent chain driven).
http://www.runningtideyachts.com/dynarig/Tennant_Hull_V_ChainDrive.php

 

Rim Drive

Or maybe a rim drive like this but driven by a 'silent chain' rather than an electrical source
https://www.youtube.com/watch?v=Te_xejpriFM

With the price of outboards these days, I might consider having a machine shop experiment with this idea.
Actually several years ago I thought about finding a Thai shop that might be adventuresome enough to experiment with this idea.

 

Nice concealed pod arrangement on this TC 11.5.

http://www.tcdesign.co.nz/TC_Design/Sailing_Designs/Pages/TC_11.5.html#6

 

Everything about that TC 11.5 makes sense.

 

Do they actually make them in 25 to 60HP?
I cannot see why one could not put one aft in a hull and one forward in the other and actually drive a cat sideways against the wind!
Couple that with electric drive and it would make the talking point in any marina....

 

Peripheral Journal Belt or Chain Drive

As far as the electrical driven rim-drive units are concerned they seem to bounce back and forth in referring to them as thrusters, most often referring to bow thrusters rather than vessel propulsion thrusters.

It seems they have a way to go before they really produce a vessel propulsion unit, although there appears to be a few propulsion unit on ferries.

...couple of subject threads I started on the subject:
http://www.yachtforums.com/threads/rim-driven-propellers.3961/

http://www.boatdesign.net/forums/propulsion/exciting-new-eps-thruster-propulsion-9432.html#post65512


If there were a nice compact electrical rim-drive PROPULSION unit I would consider having it on a new design weekender/picnic, gamefishing vessel design I am going to fantasize up for Jimmy Buffett,... in place of that monohull he has in-build. I'd supply that electric power with one of those integrated Steyr hybrid diesel electric engines.
http://www.steyr-motors.com/marine-diesel-engines/2-4-and-6-cylinder/full-hybrid-propulsion-system-diesel-and-electric/

That electric rim drive unit could be on the end of a 'stalk' and be retractable in/out of the water. It could also be rotate-able for steering it's thrust in fwd or reverse..

Until they get that electrical rim drive unit in production, how about fabricating a Peripheral Journal Propeller Drive
...using a hi-tech fiber belt, or a silent chain belt
http://www.boatdesign.net/forums/inboards/belt-drive-37290-3.html

 

Diesel Outboard, Belt Drive

Diesel Outboard
Multispeed Transmission
Belt Drive

OXE Diesel is the worlds first high performance diesel outboard propulsion unit. OXE Diesel aims to provide the market with a strong and reliable outboard unit with benefits such as diesel power head and a robust belt drive propulsion system
http://www.oxe-diesel.com/performance/

https://www.youtube.com/watch?v=1HF0SVQ_uD4

 

I've been playing with a belt design idea for an electric drive. You don't need any gears, just the pulley. I like that you can raise the whole thing out of the water by swinging it around the shaft. If you swung it up just a bit, you could get prop up above bottom of hull for some real shallow cruising.