another idiot with mad ideas, new boat build

[Divemaster1]

Rob,

Have you thought about ditching props, rudders etc., that creates drag and go straight for waterjets ?

 

[Robg71]

Mmm, sarcasm... I recognise that

 

[Divemaster1]

Well ... perhaps a bit Rob, but seriously ... Fast Patrol boats use them and have less moveable parts ... (can avoid gearbox to start).... handle both slow & high speeds ....

 

[Robg71]

I imagine they like a drink though.
What else can you tell me about them.

This is purely curiosity

 

[Divemaster1]

I imagine they like a drink though.
What else can you tell me about them.

This is purely curiosity

Why would they drink more .... they will be powered by same engines....

Basically thrust in direction of travel instead of downwards angle, so more effective, and with less drag than sterndrives....

Sideway motion possible without thrusters... simple mechanics really ... big impellor connected to engine shaft drives big impellor shifting loads of water pushed through nozzles at stern.... U shaped buckets across nozzles push water downwards (neutral) and forwards (astern) ..... mixing the two and steering thrust allow you to move sideways....

Nothing potruding underneath boat...

A bit sensitive to growth in tunnell (water intake to impellor)

More stuff in here ... http://www.hamjet.co.nz/faqs

 

[MapisM]

currently its in use in fast patrol boats, and has proven history.

Mmm... Aren't FPBs built in alu, rather than steel?
A full planing steel hull is a sort of oxymoron, in my books...

 

[MapisM]

Why would they drink more .... they will be powered by same engines....
Basically thrust in direction of travel instead of downwards angle, so more effective, and with less drag than sterndrives....

I really don't think it's as simple as that, DM1.
I've never been so interested in the waterjet technicalities, but surely there must be some relevant energy losses in them, compared to props.
Otherwise, they wouldn't be typically used only where their OTHER advantages (and indeed they have some, as those you listed, or the capability to operate in extremely shallow waters) are the key factors.

 

[rbcoomer]

Rob,

Have you thought about ditching props, rudders etc., that creates drag and go straight for waterjets ?

I think he'd quite like to ditch anything with manifolds at the moment...

 

[Latestarter1]

Well ... perhaps a bit Rob, but seriously ... Fast Patrol boats use them and have less moveable parts ... (can avoid gearbox to start).... handle both slow & high speeds ....

Hi Alf,

Water jets without gearboxes a a nausiea, they tend to shuffle, also having ability to reverse impeller great for blowing out weed.

On commercial vessels jets are just fine as all performance is at the top end, however part load is just 'orrible'.

Plus point is that one set up you can never overload a boat with jets, just goes slower, however get impeller matching wrong and engine is always overloaded.

 

[MapisM]

Plus point is that one set up you can never overload a boat with jets, just goes slower

I for one would be interested to hear more about that.
Why with an overloaded and/or badly fouled hull you wouldn't overload the engines, in a waterjet propelled vessel?
Just curious. I take your word for that, but I can't think of an obvious reason.

 

[jfm]

I for one would be interested to hear more about that.
Why with an overloaded and/or badly fouled hull you wouldn't overload the engines, in a waterjet propelled vessel?
Just curious. I take your word for that, but I can't think of an obvious reason.

It's because the water jet does not much "see" the flow of water past its impeller caused by the boat's speed. It pumps a jet of water into the open air, and the flow rate of that jet is the same whether the boat is doing 0 knots or 100 knots, whether the hull is clean or fouled, etc

Now, this isn't quite true. It is true on the downstream side of the water jet becuase that is just being squirted into the air like a water pistol. But on the upstream side, the inlet, if the boat is going fast then there is a boat-speed related push of water into the tunnel inlet, but it is nowhere near as significant as on an open propped boat, which is what LS's point was

 

[MapisM]

Doh! Not only that makes good sense, but it was also not that difficult to guess, I must admit...

 

[rustybarge]

Hi Rob,

I knew in the back of my mind that was an ocean going motorboat with a round bilge flat bottom, a serious piece of kit for off-shore cruising...

Here it is......

View attachment 34430View attachment 34431

But it does have small bilge keels....maybe too small to call keels though.

View attachment 34428View attachment 34429

Here are the specs....

http://setsail.com/fpb-64-hull-shape/
http://setsail.com/fpb-64-introduction-basic-specs/

 

[Robg71]

Thats a big hefty piece of kit. Looks like it could go to the arctic, its certainly built of stern stuff.
It looks like ali from the photos. Showing 12 and 16mm below the waterline.
What length is that ???

 

[rustybarge]

Thats a big hefty piece of kit. Looks like it could go to the arctic, its certainly built of stern stuff.
It looks like ali from the photos. Showing 12 and 16mm below the waterline.
What length is that ???

64', single engine.

 

[Robg71]

This, I like

 

[Mr Googler]

Went do you get started rob. Can't wait to see the project get underway. Saw a couple of navy seatek 600hp engines with surface drives for sale the other day and thought of you

 

[Whitelighter]

Engines Rob:

http://www.bidspotter.co.uk/en-gb/a...0000/lot-c079961b-41e0-4b03-b65a-a21a010cb4d9

 

[rustybarge]

Engines Rob:

http://www.bidspotter.co.uk/en-gb/a...0000/lot-c079961b-41e0-4b03-b65a-a21a010cb4d9

£100k each new.......don't look at the spares price list.

 

[rustybarge]

Propellor tunnels really do make sense, tucks the props right up in the hull, or even easier....single prop/skeg.

What size of single engine do you need for 25 tons/25 kts?
Some very large planing boats have as little as 50hp ton, so that would make it 1250hp.or call it 2000 hp to be on the safe side. ( you can never have too much power)