Are props the old fashioned propulsion system?

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Gludy

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Recently, I have been studying the use of water jet propulsion V traditional props.

At present, water jets seems to be winning in every aspect:-

No need to worry about nets, rocks - prop damage etc.

Constant load on the engine, not a varying load as the prop is moved up and down in the wave.

No gearbox - less to go wrong

Safer when anyone is in the water - they get, at worst a high powered shower, not chopped up.

A lot less noise, no prop shafts vibrating through the boat.

Engines last longer.

No change in performance with time due to dirty props.

Fantastic ability to move in any direction at any speed and the ability to just move sideways into a very tight berth.

Ability to, in effect heave to in a storm, with forward and backward propulsion balanced as required.

Ability to hold station in cross current and cross wind etc.

Props appendage drag accounts for about 17% of the total drag on the boat - its zero with jets.

Even a 60 foot motor cruiser can dry out with jets - extending the number of places you can visit and also allowing you to get to the hull without a lift out.

I could go on - but so far I cannot find a single advantage of props over the jet propulsion. So as a beginner to all this, I started to ask myself - why none of the big production companies use them. I find that Sunseeker tried them about ten years ago but also find it was not a real try - they did not change their hulls to suit the jet propulsion, they had problems with the control system.

I also find the RBLI are now experimenting with jets and the MOD has ordered a pile of jet boats after carrying out tests that involved putting a 30 footer onto a trailer in a 7 knot current by simply going sideways onto the trailer.

The RNLI spent days going through a pile of intentionally placed rubbish to get some into the water intake and after a number of days succeeded in sucking in a rope - they simply lifted the hatch cover and took it out. No need for a lift out, no need for a mechanic.

Many commercial ferries use jets because of the savings they make on engine maintainance plus the amazing ability in their ability to manouvre.

So are the big production companies wrong? Is the market too conservative - is their a huge resistance to change? Or am I just a beginner who is missing something? Tell me.



Paul
 
I see what you mean, see you have been reading Cara,s sales bumf I agree with all about jets, the only thing you have missed out is the cost of maintainance, also if you do have a problem then most yard would not even know what a jet is.

I was in spain working a few years back and was speaking to the Hamilton guys, they were saying about the good and bad of jets, the main factor was the cost and not being able to do any work on them yourself, if you want speed then a surface drive system may work better. I still not sure about the Cara boats, purely from a aftermarket and selling issue.

Paul js.
 
Can you expand a little on the cost of maintainance? The engines I would be going for would be two 700hp Cats, so that part is fairly standard. Hamilton jet have a nase in the UK and hold all spares etc. They also take the trouble and time to reply promptly to any queries/phone calls.

I have had to send away for any VP parts I need, VP to be fair, have always sent them quickly but then so would Hamilton.

As regards yard experience with Jets, then from ny observations, I agree this can be considered as zero. I am going to delve into this aspect of maintainance more deeply now and respond in full on this thread.

My real qestion back to you, is that having agreed with all the advantages, then assuming there was yard experience, assuming jets were known at every marina, I assume you would much prefer jets? If this is the case, then would you agree that the reason jets are not much used is not because they are not better but because, in a nutshell, the market is stuck in a prop rut - so props are used despite them not being the best means of propulsion but simply because we are stuck with them in a very conservative market place?

Paul
 
I agree,

It is also my intention to purchase the next boat with jets and cannot find any negative comments why it shouldn't be.

"Props" and the other stuff you get with them (shafts / outdrives) seem positively old fashion.

We appear to be stuck with that british attitude " we always do it this way"

I would particulary like to hear about any companies that would replace my three volvo 41's with three similar jet units?

Under those circumstances I would keep triple ace,

sealine 365, triple jets say 300 hp each = could we 45 or even 50 knots?

River use would be fabulously effective just on the middle engine, plus bow thruster but would it go like stick when needed.

any takers?







"Take control & then take the commission"

www.cleverdic.co.uk
 
No prop rut really its just that all the builders and designer tend to go for shaft drive developmets, imagine the cost of producing moulds and tooling to set up different hulls, as all new models from princess of fairline tend to only have slight mods to the moulds to create a new model, take Brooms 37 it was stretched to 39 then crudely to 41 if you look at the hull you can clearly see the join just before the rudder stocks are , so no development there at all just another bigger model on the cheap I should imagine jets cost more as well.
It alway amazes me when we go down Southampton water at say 25 knots and we are passed by the Red jets at 40 knots, alright they have 2 1000hp engines but are very heavy and full of passengers as well, then they moor up on a sixpence at the other end, my answer is that if you feel they are right for you then make a deal with them for say a service contract to see where you stand, are you thinking of just using the boat for your own pleasure or running it commercially, there will be a massive difference either way.oh and why are you at home id rather be boating myself!

paul js.
 
i must have virtually driven past your house on Friday night as I came back from my boat. I came up from Milford along the Heads of the Valleys. A40 / M50 and the like.....
I could have stopped and let you see the Salt from the Sea air still clinging to my face ........ (:-))


Adrian

Any jobs going ??
 
From what I understand, jets have incredible manoeuvrability - you can go in any of the 360 degrees at any angle and any speed you like. You can berth a 60 footer in a 61 foot space.

There is also a very good reverse thrust – as you say it is achieved by deflection, but you have the full engine power in reverse if you wish.

You really can park these boats on a sixpence. Travelling at 30 knots you can bring the boat to a stop within 1 and half boat lengths.

I can see no problem in the reverse direction at all, I think it is a myth about lack of reverse thrust – but I stand to be corrected, if you can explain more about the problem you perceive with reverse.


Paul
 
Think reality may be differant, else why fit fit bow and stern thrusters to jet boats.

Equally if the current operating system is scraped, I can see a future.


Brian
 
Dont see what all the fuss is about. I can bring my boat to a stop within one boats length if you ask me. It will also turn round on a sixpence. It will go side ways or any other direction you want it to go in. So whats fresh. Ask ToMo. Ive only got two screws. But cant think of a need for any other divices to put me where I want to go!! Cant see if what ever sort of drives stuck out of the arse end are going to make any improvement. Maybe there better cos just different. So cant complain. Just a thought and all meant in the best of tastes. <G>

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn
 
And no risk of Hydraulic lock sounds good to me ;-) Where can I get more info?

Dom


I just want my boat back in the water ;-(
 
There are differnt types of jets. The type I am talking about does not require any stern or bow thrusters and can turn the boat on a sixpence.

There have been significant developments in jets over the last 15 years or so. Most of the myths surrounding them are really out of date.

Paul
 
Maintaiance of Jets

I have now had a chance to look into maintainance of jets. but first of all I missed out on a few ealier points.

Unlike a prop boat that as the hull/props foul up over time, there is an increasing load on the engine - this does not happen with jets - the load does not change.

The approach to jets I am talking about is based on the Hamilton jets, so speaking for them - being specific about them.

The most complicated part of a Hamilton Jet is the control equipment. Even that is basic and is in fact uses almost exactly the same bits as you would have for any of the old fashioned engine/gearbox/propeller installations. The large commercial jets do require more sophisticated controls ie those in ferries in the 40-50M range.

Maintenance costs are generally low and there are virtually no special setting up procedures. Consequently, even quite a large jet can be stripped down and rebuilt using a simple “nuts and bolts” technique and I am told that virtually every boatyard that has carried out work on such jets will confirm that it was a lot less difficult than they first feared! Obviously trained engineers can do this work if required.


The impeller wear ring can be changed within a couple of hours (costs about £100). Normal wear on these rings means a normal life of longer than 5 years! You can even do this work if the boat has dryed out, so its low labour costs, low overheads and cheap.



Routine maintenance is
1. checking oil both hydraulic and lubrication dip sticks are provided at an easily accessible position
2. checking anodes.
3. checking belt drive to hydraulic power pack.
4. check for blockages
5. check water seal - for which a “tell tale” is provided

No gearbox, less likey to foul etc, etc all means that as it is appearing to me, Jets are the most logical way to go and work out low maintaiance compared to the 'old fashioned' prop route.




Paul
 
Reverse with jets

I have checked out the situation regarding reverse thrust.

With modern jets you can get about 60% of the forward thrust in reverse, so thewy are far better at reverse than prop jobs. The old jets from years ago just had a baffle that the jet hit, modern jets redirect the thrust and hence achieve a far better reverse thrust than any prop job.

You can also throw this power into reverse instantly without harming anything - mind you, with this braking power you would need to watch the natural momnetum of objects such as the crew who could go flying through the front windows and of course the engines with a ton or so of weight!!

Paul
 
I could not agree more - the production boats folks have a huge intertia against changing their moulds and adopting anything new - hence the market needs to start to demand more, that is the only way they will change.

So far in this discussion, all the raised points have done is confirm my growing conviction that jets are so very much better for the leisure market than props.

To this time no point has been raised that does other than support jets. Those that have been raised such as low reverse thrust applied yearsd ago, today the opposite is true!

Paul
 
Re: Reverse with jets

I'm glad to hear that my observation re reverse is outdated, my experience was with an older boat. Cray fishermen (lobstermen) like the jets as the chance of fouling a pot warp is removed to a large extent.

You might just be onto a winner!

Cheers.
 
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