Pirate 21 with jet drive

Discussion in 'Jet Drives' started by ruurd, May 8, 2011.

  1. ruurd
    Joined: May 2011
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    ruurd Junior Member

    Hello all,

    I am considering buying a pirate 21 with mercruiser 165 hp diesel and a pp90 jet drive.

    The boat is doing 13 knots according to the owner. A new impeller is installed 3 years ago and not much used.

    This boat is 21 feet long and has a good shape.

    I think it should a least do 25 to 30 knots with this engine and jet drive am i wrong?

    Thanks for your answers,

    Ruurd
     
  2. anthony goodson
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    anthony goodson Senior Member

    No you are not wrong ,I don't know this hull ,but given that it is typical weight and shape ,it should perform as you say ,at least. I do however know this jet very well and although it was designed thirty years ago it is in my opinion still the best jet of it's size available ,and is very well matched to this engine and hull size We need more detail of the operating parameters that you are experiencing ,basically what mechanical conditions you have at WOT and during acceleration. ,revs ,noises, etc, and also who supplied, matched and installed the new impeller,and the performance prior to this. I assume it is a PP90A ,rather than a G ,not that this of great importance but it is as well to know. A brief description of the hull lines ,might be useful ,deadrise etc.
     
    Last edited: May 9, 2011
  3. baeckmo
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    baeckmo Hydrodynamics

    Yes, I agree with Anthony on the PPjet; it is a shame that Vosper Thornycroft couldn't come up with a decent marketing strategy when they bought out Mr Parker! Now most of the tooling is scrapped for one of the best jet designs there has been on the market.

    As to the problem here, my instant reaction is that there is an air leak; check that the inspection cover is provided with a correct rubber sealing ring, and that it is seating evenly all around (loosen the two holding nuts and retighten them little by little in equal steps).
     
  4. ruurd
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    ruurd Junior Member

    Thanks for the quick reply 's. I have some pictures of the jet drive and engine. Details on the drive i will get later.

    I can't give any running parameters because i don't own the boat yet.
     

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  5. anthony goodson
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    anthony goodson Senior Member

    Well thats a 90G {glassfibre body } which is slightly rarer ,that boat looks heavy . Could you find out the gross weight of the boat ,and the revs at which the mercruiser develops 165hp.? Good afternoon Baeckmo ,nice to have your company here, last I heard Naiad are now producing the 90A ,there is a picture on their website ,still looks good after all these years. I am currently at home in Murcia if I go missing blame my dodgy internet connection.
     
    Last edited: May 9, 2011
  6. anthony goodson
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    anthony goodson Senior Member

    Some more pictures of the hull would be useful ,particularly of the planing area aft and the jet intake if possible. The more the better.
     
  7. anthony goodson
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    anthony goodson Senior Member

    Don't worry about the engine details ,a closer look at the picture told me it's a d-tronic.
     
  8. ruurd
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    ruurd Junior Member

    The boat is actually a MI 21. This was manufactured before pirate took over building this boats.

    I think there are no big differences. Boat weighs somewhere around 2000kg maybe more with this diesel engine.

    Today spoke to the pirate manufacturer and he said the boat with a 165hp jet drive should be seen as a 100hp engine because of the power loss in de jet.
    Even with a 100hp engine it should make 26 knots he said.

    The guy that's selling the boat is confident about the impeller because he changed it for the customer himself. He says the only option is to buy a 300hp inboard engine on this boat to get it faster. I think in the years they are sailing with it, it never sailed any faster.

    ---
    Just called a guy selling the same boat in Ireland with a Ford mermaid 170hp on a jet drive system.

    His boat did only 18knots max. He said the same as the manufacturer about the jet system that consumes a lot of energy and was the reason on his boat to do only 18knots.

    Probably the combination on this heavy boat is the reason for the slow speed.

    The cheapest option should be to convert the jet to a sterndrive i think.
     
  9. ruurd
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    ruurd Junior Member

    Some more pictures

    Here you can find more pictures on the pirate 21 which is slightly different.
     

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  10. anthony goodson
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    anthony goodson Senior Member

    My original comments were based on an assumed, much lower weight , 2000kg plus crew gear etc is too heavy for this jet ,whatever horsepower you put through it. Whoever put this combination together should not be proud of the fact that they have made a contribution to the bad reputation that jet's have. So much wasted time ,so much wasted money, totally unneccessary. A nice looking boat ,it deserves re-powering with a shaft or a leg ,good luck with it.
     
  11. ruurd
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    ruurd Junior Member

    Thanks for your info anyway. I also think it's a nice boat and still interested to buy it.

    What do you recommend on this boat. Is it a good option to connect a stern drive on it with the same engine?
     
  12. anthony goodson
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    anthony goodson Senior Member

    Your biggest problem may be the big hole that a PP90G will leave in the hull when you cut it out ,not just in the transom but in the hull itself, you may be suprised just how large it is. You will also need to extend the engine bearers aft over this area ,not a job for the faint hearted. The D-tronic has its faults but since you already have it I would keep it, fairly easy to mate to a leg. There are others on here with more experience of legs than I, hopefully someone will chime in ,or if not start a new thread. Think carefully about all this work before you buy.
     
  13. baeckmo
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    baeckmo Hydrodynamics

    Difficult to see any details regarding the planing surfaces; are there any steps or spray rails?

    Some time ago I used a PP90 together with the 250 hp VM - Mercruiser engine for a series of tests regarding inlet shape. The boat was an alu monohull, constant deadrise 17 degrees and a test weight of 2540 kg. Max speeds came around 31-32 knots at full power, 3600 rpm. At 3170 rpm, where the power absorbed by the PP would be close to your 165 hp, we had just below 26 knots.

    This seems to be about the maximum weight/power to be used, since quite small additional weight created problems getting over the hump (hump resistance max at ~14 knots). I would say that 2000 kg is a reasonable maximum for 165 hp + PP 90.

    Either the MI 21 is terribly overweight, its bottom shape has some bad features, its center of mass is way off, or the engine - jet matching is not ok. Before you enter on any rebuilding projects, let's see better pic's showing the bottom shape!

    Another reflexion; this engine is a good one, but there is one issue that you should be aware of. The intercooler tube bundle is mounted directly on top of the openings down to the inlet valves. Any untighness (corrosion of sealing surface, bad soldering et c.) in the bundle will cause cooling water dripping straight into no 4 (or 6) inlet. Engines produced around 2003 have been found to have intercooler pipe bundles with defect solderings. So before making a deal, check that the engine can be rotated without sticking in any position; if in doubt get someone to make a compression test.

    One more thing on this engine; as most Italian engines it has a very effective cooling system, it also has a temperature switch that limits injection volumes (= output power) until the engine has reached the correct working temperature. In cold climate this has been a source of frustration, as the engine never came up to correct temp. We had to bypass a portion of the raw water on one engine before we found the culprit (and that was on a jet installation.....).
     
    Last edited: May 10, 2011
  14. anthony goodson
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    anthony goodson Senior Member

    I am sure your figures are correct Baeckmo,as they always are, and a very useful guide to expectations here but in my experience a 90 only works well up to 2000kg gross. Your figure of 26kts max ,in practice ,means that there is no "on plane" cruising speed at about 3/4 throttle ,at that weight it will drop off the plane very quickly as the revs are reduced, this will mean a very unpleasant and inneficient boat ,not a project I would want to persist with. We are assuming here of course that this boat is well in excess of 2000kg all up ,perhaps an accurate weight would be useful.
     
    Last edited: May 10, 2011

  15. ruurd
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    ruurd Junior Member

    I don't have better pictures on the boat. Also engine running data not available. The owner already send me a lot of pictures. He said the boat is "just in plane" at full power"
    I really should take a look my self to get a better picture.
    Problem is the distance. But it could be a bargain.

    I cannot find much info about the boat's weight on the internet. It is made in the UK by Marine Installations. Now called Pirate.

    I added another picture where you can see the "steps/spray rails" on the hull.

    Maybe it's possible to add trim tabs? As I understand from baeckmo the boat is at is highest resistance around 14 knots (different boat of-course) and that is just the speed it sails now. If you could get it through the "bump" it should go faster.

    Do you know what should be a reasonable price for a "project" like this. (Based on the pictures)
     

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