Water Jet on a sailboat?

[Polarity]

Hi all,
Would a jet drive be feasible on a sailing yacht ? - I can find no reference to this anywhere on the net - except a magazine article by David Gerr that so far I have not been able to get a copy of.

I am in the planning stage of building a 14.5m steel sailing yacht, hull construction to start in the spring. -
http://www.tedbrewer.com/sail_steel/miami.htm is the base design to be stretched 5%.

I can think of several possible advantages of putting a water jet drive on her namely - less drag, no lines to clear, more manoeuvrable (single hander!) and as my plans involve high latitudes - less underwater bits to wrap ice around.

A prop/engine calculation comes out for an 85hp, 2000rpm, 1.94:1 reduction engine/gearbox to use a 25x17 , 3 blade prop to give 8.7Knts. The prop thrust/bollard pull of this is calculated at 722 / 915 Kg

Any idea what kind of set up would be required, does it exist, has it been done? I can see the cost of the jet ofset against the drive line, smaller (or no) gearbox, folding prop ($$) etc.

I gather - from the complete lack of information this would be pretty groundbreaking - but what a market to open up for someone if it were feasible.

Any thoughts or resources would be apreciated.

[Stephen Ditmore]

Most jet drives are optimised for planing speeds and are not efficient at displacement speeds. A possible exception is the Trakktor Jet from NAMJ <http://www.marinejet.com> but this is a heavy, transom mounted unit, and without a way of pumping the tunnel dry when not in use it becomes even heavier. As you may know, it's important to concentrate weight amidships on sailboats to reduce pitching. What I did show in a design contest entry (my boss's entry beat mine) was a (bow) thruster acting as a propulsor with the tunnel incorporated into the back of the centerboard trunk. Several companies (Schottel is one) make thrusters that do double-duty as propulsors, so something like this could work.

[Stephen Ditmore]

Having said all that, I'd be hesitant to advise you to innovate in this way on your basically conservative Brewer design. Yanmar Saildrives are great for racer-cruisers, but in my opinion a cruiser like you is better off sticking with a basic inboard arrangemet and getting an Autoprop <http://www.autoprop.com/>.

[Stephen Ditmore]

For steel coating links see http://boatdesign.net/forums/showthr...p?threadid=287

[Gades]

As Stephen said before, waterjets are just for planning hulls. If you contact a waterjet supplier, and give them a couple of details about your project, they´ll be honest with you and will tell you the same thing. Once I had to find out if waterjet was good or not for a project, and believe me, you don´t need it. But also, I don´t know about the one that Stephen has mentioned in particular.

The office were I was working at, was involved in a 70 footer for high latituted, and they did never think about waterjet. They did have some thoughts about quite a special hull shape, that would be able to protect the propeller, and a very important thing is that both the keel and the rudder should be lifting ones.

If you need some more advice, you should look for some information about Skip Novak, I don´t remember right now his web, but if I do later, I´ll post it here.

Te deseo buena suerte con tu proyecto.

[Gades]

OK, this is the one:

http://www.pelagic.co.uk/

Here is Skip Novak's site: http://www.pelagic.co.uk/

Oops - timing is everything!

[Stephen Ditmore]

One thing you might consider is a retractable bow thruster that can be turned 90 deg and used as an aux. propulsor should anything happen to your prop. Also, you might want to consider positioning a secondary sea chest above the prop extending above the waterline with an access plate at the top to allow you to service the prop, and whatever seawater intakes you might want to attach here. Realize, though, that the prop will exert forces on the hull just above it, so any trap door or grate you might want to position there will need to be strong.

[Polarity]

Thanks Stephen y gracias a ti tambien Fernando. - OK you talked me out of it - I don't have the cash to be too innovative!

The Pelagic site was interesting and another one added to my book mark list that I will eventually get around to putting up on my site!

I checked out all those coating sites - lots of interesting stuff. Especially the Ceram-kote 54. The ZetaN looks pretty radical - anyone have any experience with either?

Not sure about the sea chest - I could possibly use it to clear a line but I'm not sure it would be feasible to remove the 25" prop or effect blade repairs - drysuit time brrrrr.

Dont have plans to put a bow thruster on her, - on my yawl I use the mizzen!
Interesting thought to use one of those retractable stern thrusters that I have seen - but then it would have to be a diesel electric/hydraulic set up and I would think the complexity would go way up.

Thanks all - I'm sure I'll have a bunch of more sensible questions!

Paul
SY Polarity

[Gades]

Hi Paul,

I´m glad you made up your mind a little bit.

Now, I´d like to ask you something, what made you choose this type of hull?

And what considerations are you taking into the design/construction of it?

Somewhere at home I have a paper with the main points you should take care of when you´re talking about a similar project as yours. So, if you are interested in it, I´ll post it when I get back home from Christmas holidays.

[Polarity]

Hi Fernando

Yes please I can use all the help I can get! - I'm sure other board members would be interested too.

As to why that boat? well so far...

I am looking for a cruising yacht for serious offshore, single handed, cruising - including ice and high latitudes (Single handed N.W passage anyone?...)

It almost certainly has to be steel because of strength, reparability, and (significantly) cost. I have a contact in Poland who will be helping organise the construction of the hull at the yacht division of a commercial shipyard. If money was no object I would seriously consider Aluminium - but the potential for weld problems worries me.

The Ted Brewer design is to be stretched to 47.5ft as part of the digitisation of the drawings and the long keel replaced with a fin and skeg. She is also to have a pilot house on her - Ted has actually combined 2 of his design to make one. - and of course one of the most important things, I think she is very pretty!

I appreciate that a number of high latitude yachts have lifting keels / rudders. However as an boat engineer my philosophy runs along the lines of - "the less moving parts in close proximity to saltwater - the better" (see the start of this thread!).

To me, with a swing keel on an alu. boat getting the right amount of ballast down there to make me feel comfortable enough for Cape Horn (or the Bay of Biscay for that matter) is a lot easier than the same concept in a steel boat. I looked at the boat used by the Northabout team (www.northabout.com) and considered that it was a big price to pay for 65cms of draft.

Also I could not afford (by a factor of up to 10!) plans by (mentioning no names) Naval Architects that have built dedicated ice machines previously.
I am considering a false "ice breaker" bow though to help lift her up onto the floes - should it be necessary.

In terms of construction I have re-laid out the interior to give a watertight bulkhead 21% aft of the bow giving a big forepeak/ anchor locker, a separate workshop area, and the usual single handed amenities for the interior.

I like the ketch rig - if one falls off you always have a spare! Seriously though I like lots of places to hang sails, radar and look out from, the cutter rig means that I have a great heavy weather combination with the stays'l and mizzen. The mizzen is also great for docking (at least on my underpowered, clipper-bowed Yawl it is!). Still working on the running rigging layout.

Enough already! - Thats more or less the thought process so far but I am always open to suggestions!

Paul

[Stephen Ditmore]

The ideas at Origami steel yacht construction might be worth a look (not that I find any fault with your thinking, or with the Brewer design). I don't know if you'll be able to use the following link without registering at
http://groups.yahoo.com/group/origamiboats
first, but try
http://groups.yahoo.com/group/origam...SwainModel.gif
for a pattern from which you can build a model.

Also, check out Design Question

[Polarity]

Steve

I agree with you about the nuisance of getting into that Origami boat forum - took me half an hour !- @#$!ahoo grrr...

Interesting idea but only seemed to work up to about 40ft though

In fact one of the things about Teds design is that it is a radius bilge design so theoretically it should be simple to build.

I love a good theory...

Cheers

Paul

[Polarity]

BTW I really like Michael Kasten's site but I had missed the article you mentioned:

http://www.kastenmarine.com/caution_note.htm

... But having read it ...I got the hint!

Paul