Back with Jets and some answers

[Gludy]

Re: Jets

Floating fridge was not hit in the Marina - it was hit in the centre of the Bristol Channel!!!!

Out of the last three trips I know about of friends to the Channel Isles - all three have hit something - one knocked the prop on a rock - one hit a fishing net and sheared gearbox shaft - one hit a thick rope!

Even the Motor Boating Video set where they teach the day skipper in part 1 and send the beginners off to CI's in part II - they hit a 40 foot tarpaulin!

Soi anything that has no bits sticking out is a big plus for me.

Paul

 

[wakeup]

Re: Jets

I think i've seen that video.

It is the one filmed in the eighties with the wife with the very bad dress sense.

I seem to remember that the camera man just happened to have his scuba gear handy and was able to go in a cut away the tarp from the props.

Mind you if you hit a fridge at 28 knots I think you would have a problem anyway with jets cause I would have thought that could put a hole in your hull.

yada yada..

 

[Gludy]

Re: Jets

Yes - thats the video and yes the cameraman saved the day.

You would probably put a hole in your hull but you have a greater chance of survival hittting something like that without any appendages to rip out. The boat I am looking at has a mere 70cms draft, so there would at least be cahnce of glancing over the top of something. It when the A bracket and props hit that it could just tear it apart.

I agree about the dress sense!

Paul

 

[wakeup]

Re: Jets

OK so back to jets.

The boat you're looking at only draws 70cm?

Wow that seems very shallow for a 60 ft board which leads me to my next question.

Is the deadrise a critical factor when selecting jets? Ie does it need to be shallow so that the boat has completey steering neutral. Obvioulsy the lower the dearise the poorer the sea handling or does this issues go away with jets in terms of directional stability? And how about ride, I guess a shallow deadrise is gonna limit sea use to smooth conditions only? And what about the intakes, is the position critical (through hull I guess). Are there other side benefits, I would have thought you could do away with trim tabs, is that so?




yada yada..<P ID="edit"><FONT SIZE=-1>Edited by wakeup on Tue Jun 25 14:21:52 2002 (server time).</FONT></P>

 

[Gludy]

Re: Jets

"Is the deadrise a critical factor when selecting jets? " - no I do not think so.


"Obvioulsy the lower the dearise the poorer the sea handling or does this issues go away with jets in terms of directional stability?" The boat can do 15 knots into a force 8 and 30 knots with wind abaft the beam in a force 9. It is a pilot boat hull that had the Nelson pilot boats turning back when going out in a force 8 and it succesfully landed a pilot onto a big boat doing 16knots then came back to port at 30 knots!!! So sea handling in exceptionally good as is resitance to wind - the hull has a lot of steerage.

"? And how about ride, I guess a shallow deadrise is gonna limit see use to smooth conditions only? " No - in rogh seas a far better ride than any planing hull boat and made for rough conditions. In a big sea, you do not need to hold onot the wheel for dear life either - just a slight adjustment every so often.

"And what about the intakes, is the position critical (through hull I guess). Are there other side benefits, I would have thought you could do away with trim tabs, is that so?
" - Yes you no longer need trim tabs. Nor bow thrusters.
Water is sucked in from the bottom of the hull upwards - there are no protuding bits.
There is always a constant load on the engines - they do not vary, even in a big sea.
However, the jets need to be designed properly into the boat as an integrated whole. Hamilton will advise anyone on all this.



Paul

 

[wakeup]

Re: Jets

I am beginning to get it.

So is the set up a bit like some light aircraft I have flown that have a CSU (Constant Speed Unit) where the engine is set at the same throttle setting and you vary the manifold pressure to get more or less performance out of the aircraft.

If this is the case then is woul be a BIG adavantage especially listening to all the stories about blown V#L# engines. This approach is much kinder indeed to engines and they are less likley to blow up.



yada yada..

 

[Gludy]

Re: Jets

Yes- you have two sets of levers - one throttle, one for comtrol of vectoring.
You can set your throttle to any level you like - then in the Marina - leave it.
Your jets are now going but in balance holding your boat still.

To now just use the other levers to control forward/backward vectoring and the wheel. To go 100% sideways just steer your wheel to give the 90 degrees whilst controlling your speed in the 90 degree direction by your vectoring levers.

You can put a 60 foot boat into a 61 foot space - even in a cross wind etc.

On the latest version you have totall 360 degree control, no dead bands.

You can move at any of those degrees with you bow pointing in any direction.

Out at sea you put the vectoring fully forward and then just increase your throttle levers to give you the power you want.

See a fishing net at the last minute - it just goes over it.

Because the load on the engine is always EXACTLY constant for a given throttle setting regardless of you going forward or backwards - regardless of the waves - you have a totally constant load on the engine - no vibrating shafts, no gearbox, very low noise and all in a hull that is rated about the best out there for sea keeping.

On top of that it is cheaper to run.


Paul

 

[Gludy]

Re: Jets ,unit 4a

Chippie - yes the head office and manufacture is in NZ but they have bases in UK and USA both holding all parts and people who can really answer questions - I find that very unusual in the Marine world.

I really must stop typing these posts so fast and making all those typo's

Paul

 

[tcm]

Re: computers

I just LOVE the way you explain boats (simple things) by using analogies from the computer industry!

 

[wakeup]

Re: computers

Well TCM i'm afraid its all I know!!

Compared to V#l# powered boats, computers are simple things, more reliable, cheaper to run and the spare parts are cheaper also. They also breakdown when you stop them suddenly with the computer version of hydrolicing

yada yada..

 

[Gludy]

Storebro Confirmed

I have just had it confirmed from Storebro that they are now offering a jet option on their larger boats! It seems that the twinkle of dawn is slowly opening up on the horizon!

Paul

 

[jfm]

Re: That Caramarine boat

Gludy, I looked at the Caramarine Website. (I know of the firm well, I'm often in Carrigaline). It didn't contain any data. Where did you get your data from - if it's from Cara, I would guess (correct me if I'm wrong) that it's all a bit theoretical, becuase boat # 1 is still in build. I would be cautious about non-proven data that is perhaps a bit implausible.

 

[Gludy]

Re: That Caramarine boat

I have received info from Caramarine but they have now started selling boats - I know of one that has been collected and is now in Southhampton - the owner I know returned a new Sunseeker. I know of two more boats now completing build.

The data has come from the boat actually being used.

The web site is very out of date and there have been a number of major changes to the prototype shown there.

So things have moved on a lot since boat 1.

If you have any more information on Cara Marine, I would be very interested.
KJind regards



Paul

 

[Guest]

Re: Storebro Confirmed

standby for articles in MBY on Hinckley T29C (September), WallyPower 118 (Oct), AB65 (Nov or Dec) - all have jets, & should have reasonably well researched jet info - will try to answer some of your Qs in the text.

If anyone likes the Targa-style, potting shed on water motor yacht, a Finnish company called Minor make a similar boat to the Targa 31 with KameWa water jets - the guy from KameWa gave me loadsd of facts and figs on jet efficiency and advantages over props which I can dig out were it wanted. Targa may be introducing jets to their boats too.

 

[Gludy]

Articles on Jets

I am more than pleased that mby will have articles on jets.
Is there any chance at all of looking at the Hamilton water jet system? Or even the 60 foot Cara Marine boat with jets that uses the latest Hamilton system and achieves 34 knots with just twin 700 hp Cat's.?

I am certain both companies would cooperate fully - even if it just some questions to them answered in the text. Although a proper review would be brilliant.

Its jets as a replacment in 28 to 60 foot cruisers that, in my view, offer much to the boating public.

Also dig out that info and spill the beans.



Paul

 

[Gludy]

Articles on jets

For information:-
The Storebro Grand Series No1 is offered with water jet drives as an option.
The boat will then have 2 x MAN 1050 hp diesels with KAMEWA/FF450S water jet units. They have already delivered one boat with these jets.
It might be worth a phone call to them to ask them for their views as to why they have offered this option and what they see as the advantages/disadvantages.


Paul

 

[Deleted User YDKXO]

Draft (draught?)

For most planing hulls without a keel, the lowest point is the props so the draft is an indication of the depth of the props not the deadrise of the hull. In any case, I dont think deadrise at the aft end of the boat is necessarily an absolute indication of seakeeping. Certainly, a soft ride into a head sea is more determined by the deadrise further forward, the rake of the stem, weight distribution and probably a host of other factors that only a naval architect can tell you about

 

[Deleted User YDKXO]

Storebro 62 with Jets

This boat was tested in MBY issue June 2001. Whilst being very complimentary about its low speed handling the MBY testers were'nt so happy with its handling at speed. Apparently it heeled badly at speed in a crosswind which the testers put down to having to constantly steer into the wind due to the lack of lateral grip (normally provided by the rudders) and the rounded shape of the hull, a characteristic which was stated as being typical of jet powered boats. In addition, not having trim tabs meant that the hull could'nt be tabbed down into a head sea so the testers thought the ride was actually worse than a conventional boat of the same length
If you get a ride on the Cara, I would be very interested in your report because, like you, I think the advantages of jet drives over shaft drives make the system worth considering. Its going to take one of the mainstream UK builders to introduce a 40' flybridge boat with jets, though, before jets are going to be widely considered in the UK market

 

[Gludy]

Re: Storebro 62 with Jets

Thanks for your interesting post.

Your remarks about the Storebro are interesting. I will look out the issue.

Unless the hull design is for jets, just providing jets as an option, does not work well.

The Cara boat has a hull that has high directional stability - a vital ingredient for a pilot boat. I was told that this directional stability was essential if you were going to use jets and your remarks back this up.

I totally agree that it need a major 40 foot brand with jets before the market will really take a look at jets. The problem is that they do not like changing their production line and so just offering jets as an option as Sunseeker once did does the image of jets more harm than good.

It needs a major brand to offer a 40 footer designed for jets. I know Cara made smaller boats - if they produced a 40 foot version designed for jets ... that would be a help but until someone small like Cara make an impact - just as they did in the Pilot boat market, none of the major brands will move.

Paul

 

[Deleted User YDKXO]

Costs v Benefits

Even if somebody introduces a mainstream jet powered boat, the big argument in favour of jets is going to have to be a cost one ie. the extra fuel efficiency v the extra cost of fitting them relative to conventional drives. I just dont see punters forking out extra money just to get the marginal benefits of superior low speed handling and damage avoidance unless the reduced fuel consumption covers the extra cost in a relatively short period of time
Jet drives have been around for a while and, perhaps, you would have expected one of the jet drive manufacturers to at least have come up with a prototype 40 footer by now so maybe the cost benefit doesnt work out for smaller boats