Engine to suit PP jet

[JamesN]

I have just acquired a Dateline Bikini which was fitted with a 1.8 ford diesel
driving a PP jet.The previous owner installed the diesel after wrecking the Rover V8 that was previously fitted .
The diesel only gives about 18 knots so it seems to me it is well under power at only about 60 hp,so my question is whether the TD version of the 1.8 would sort it(90hp)or is there likely to be a rpm issue with the diesel as opposed to the petrol driving this jet drive?
A ford petrol 1.8 would slot straight in but I would prefer to stick with diesel if possible.

[Quicksilver]

Personally after looking up all the said parts, it seems you really ought find a rover v8, the 1.8L ford from the escort car, is entirely unsuitable, I dont know what the previous owner was thinking.

A jet unit is designed around certain parameters, rpm and horsepower. Mostly rpm, horsepower has more to do with weight. Your boat should run around 35mph, with the rover v8. 35mph is most likely the most efficient rpm and speed for the vessel. The rover v8 puts out about 160hp and 200ft lbs of torque at over 5000rpm

The ford diesel puts out 60hp and 117ft lbs of torque at 2000rpm

Huge difference!!

So the question is what diesel can do this?

On that note, I've used up my googling ability, being I actually knew nothing about these motors or that particular jet drive until you asked. It's ok I'm young and always wanting to learn more, so it's all fun to me.

I would ask "what diesel is the equivelant of the petrol rover v8?" in the diesel forum, simply being what I found leads to a whole new question.

Also try using google yourself for that very question, it appears this forum is archived for quite a while the answer might already be out there, but then I would still ask.

Try finding out exactly what rover v8 the boat had in it. There seems to be quite a few made and my figures represent more of a rough estimate. The motor went up to 200hp, from what I found.

Good luck

[JamesN]

I am guessing the rover v8 was probably around the 130hp mark.
If I put a petrol engine back in i'm more inclined to go for a 1.8 (to give around 120 hp)four cylinder which seem to be common in these hulls.

I presume the rpm of a diesel driving the jet drive is a limiting factor with the impeller fitted,but i'm not certain as I have no experience with jets..

[Frosty]

That must be quite an old boat. I remember those around 30 years ago and then they had the Ford V6 from the Granada 3 litre.

I certainly wouldnt skimp on power I would put in the biggest I could with the room restrictions.

There are some diesels around now that can easily run at 4000rpm all day, you might need a tad more than that.

[Quicksilver]

Originally Posted by JamesN

I am guessing the rover v8 was probably around the 130hp mark.
If I put a petrol engine back in i'm more inclined to go for a 1.8 (to give around 120 hp)four cylinder which seem to be common in these hulls.

I presume the rpm of a diesel driving the jet drive is a limiting factor with the impeller fitted,but i'm not certain as I have no experience with jets..

You must keep in mind the power loss of a jet drive. I mean maybe you can use a four banger, but being what I found on the PP drives, I didnt see one that didnt use a V8.......I'm sure theyre out there. Remember torque horsepower and RPM. Cannot just go on HP. Theyre must be a reason they chose a V8, I'm guessing mostly torque and RPMs.

[JamesN]

I have spoken to Vosper Thornycroft who said there were four impeller options for that jet: Ford 1600 4cyl 80hp 5000rpm
3 Ltr V6 125hp 4000rpm
3 Ltr V6 125hp 4500rpm
2 Ltr 4 95hp 5000rpm
I need to have a look at which impeller I have,then engine shopping...

[Frosty]

Well your not wrong but there so many engines that would do,I would go for a light weight Japaneese job. But to restrict your engine choice simply because of an impeller!!! how much is an impeller? It wouldnt hurt to replace the impeller anyway.

Have a word with lancing marine Southhampton, they sell engines and all the bits for anything. They have a web site--Google it.

[JamesN]

I agree,I was just reciting VT's options that would have been fitted originally in the Dateline.
The impeller is in good nick and a new one would cost half of what I paid for the boat
I'm pretty sure I need 5000rpm which gives me alot of choice.I'm leaning towards Zetecs which are in plentiful supply and also I know they will sit straight in to the mounts already in place.

[tri - star]

Please, please...Quicksilver.
Stop repeating that Urban Myth; that Jet Drives are inefficient.

Basic science invalidates this common belief.
There are some jets that don't work very well. This is true.

And a lot that easily exceed anything an ordinary prop can do.
Don't take my word for it.
Check out Vosper Thornycroft, Rolls Royce and Kamawa.
- And the fast warships, built in places like Sweden and Norway.....

There are lot's - and lot's .....of badly designed, backyard specials
out there. With the wrong engines - hooked up to the wrong jets.
That are over weight. Which only helps to perputate the myth.

Seldom is the blame is placed on the " designers " of the poor vessel.
No; most be: "...that ther...confounded jet..! "

The vessel being described seems to be on this list.
If brought back to original spec. It will definately run a whole lot better.

Although, frankly, if the cost of an impeller gives one pause.....
The phase, " Penny wise - Pound foolish." comes to mind.

Cheers !

[JamesN]

I'm not going to replace the impeller for the sake of it,it's the engine at fault.I have seen plenty examples of these hulls with various powerplants from 1.6's up to 3.5 V8's that work fine.I'll probably go for something in the middle.

[Quicksilver]

Originally Posted by tri - star

Please, please...Quicksilver.
Stop repeating that Urban Myth; that Jet Drives are inefficient.

Basic science invalidates this common belief.
There are some jets that don't work very well. This is true.

And a lot that easily exceed anything an ordinary prop can do.
Don't take my word for it.
Check out Vosper Thornycroft, Rolls Royce and Kamawa.
- And the fast warships, built in places like Sweden and Norway.....

There are lot's - and lot's .....of badly designed, backyard specials
out there. With the wrong engines - hooked up to the wrong jets.
That are over weight. Which only helps to perputate the myth.

Seldom is the blame is placed on the " designers " of the poor vessel.
No; most be: "...that ther...confounded jet..! "

The vessel being described seems to be on this list.
If brought back to original spec. It will definately run a whole lot better.

Although, frankly, if the cost of an impeller gives one pause.....
The phase, " Penny wise - Pound foolish." comes to mind.

Cheers !

Firstly if you look at any of my posts you'd see I'm all about jet drives, why else would I be posting. I mentioned a jet CAN be inefficient at slow speeds, which is a fact. Secondly I stated I recommend a beefy motor so he can get the jet to the optimum rpm. Jet are efficient at high speed, not low speeds, so if hes trying to be fuel efficient, using a tiny diesel might end up being less economical than a V8, since the jet needs to be going fast to be efficient. I believe you twisted my words. Read slowly, it helps.

I dont build real boats, I build model boats but am also a boater in general. Currently I'm building an experimental model jet boat with a variable nozzle, pretty much trying to make a very fast jet boat. Thanks for asking first in a PM or something.

This site is starting to get to me, either no one replies to my posts, I get bashed or never thanked. Why do I spend so much of my own free time trying to help....I have no idea. In all don't jump on me, with out being able to back it up.

[Quicksilver]

Originally Posted by JamesN

I'm not going to replace the impeller for the sake of it,it's the engine at fault.I have seen plenty examples of these hulls with various powerplants from 1.6's up to 3.5 V8's that work fine.I'll probably go for something in the middle.

Sounds like a good plan, from what I read somewhere, the impellers for those PP drives are like 500$ US. Might want to just have it repaired, it could help quite a bit, any nicks are going to create cavitation, which will slow the boat or at least burn more fuel. Might not effect it a ton, but I'd get an appraisal for a repair at least.

[JamesN]

about $750 for a new impeller
I've inspected it and it's in good condition,just one slight dent that won't take much to dress.I have my Tig at the ready for any nicks that I should inflict

[tri - star]

To Quicksilver,

sorry to upset you.
But the direct quote from you is, ".....the power loss of a jet drive."
Hard to take your statement, any other way, than how you say it.

Your subsequent post, makes it more clear...your intent.
Maybe.....we both need to get away from the computer for a while.

Rest easy Lad.

Cheers all !

[Quicksilver]

well from this stand point, you do have to put more hp to a jet drive than a standard drive, I thought this was a known thing. Look at jet drive outboards. Go yamaha's site for instance. 115hp motor labeled as an 80hp jet. It's the other points where jet's excel, acceleration, draft, and no exposed running gear. Theyre not exactly built because they're efficient. I know I'm kind of double talking, but I'm using efficiency as an absolute. It's not like they're gas guzzlers, but you don't put them in a boat to save money on gas, lets put it that way.

This is what I meant when saying power loss, you need to put like 30% more power into a jet to get out the same as in lets say a stern drive. Doesn't mean it burns 30% more fuel necessarily. Like my model boat, goes about 25mph+, but if I used the same motor, with a surface drive I could break 40mph. I still love jet drives.