PP65 upgrade

Discussion in 'Jet Drives' started by Michael Denner, Aug 28, 2018.

  1. Michael Denner
    Joined: Aug 2018
    Posts: 4
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    Location: Calne

    Michael Denner New Member

    I have a West End Marine ~Striker II from what I gather from this forum it’s a copy of a Dateline Bikini. The jet drive has West End embossed into the reversing bucket but to all intents and purposes it looks like a pp65 except the access hatch is square and hinged rather than round and bolted. Anyway I've had the boat a number of years and it goes quite well, when I bought it the engine was completely shot big end seized up so over that winter I stripped and reconditioned it. it’s a 3L Essex V6, to cut a long story short i increased the horsepower from the stock 140 to about 220, Big valves, upgraded valve springs, hardened valve seats, high lift stage 2 piper cam, inlet manifold with three weber carbs, steel timing gear, crank re-grind, re-bore, new pistons etc engine runs great. But the boat's performance is sluggish to say the lease, well compared to other jet boats I’ve ridden anyway, it does get up to 25+ mph eventually but the engine is revving its guts out 5500RPM with more room to go on the throttle but i daren't push it that high so as not to over rev the engine. Basically I have to open throttle slowly or i get cavitation and go nowhere fast. In order to get up onto a plane i have to open the throttle in three stages and let the boat catch up. It seems to take between 20-30 seconds to get up onto a plane. Once on the plane it does go quite well but i need more thrust in order to get a skier up or tow inflatables and thrust seems to be something it lacks. It seems with the mods the engine is too powerful for the jet, and the intake diameter seems rather small compared to the outlet nozzle, is it a case of being unable to suck in enough water? That’s what it seems like. I have adjusted the three bladed impeller so that the blade tip clearance is about 0.5mm-1.0mm can't get it closer without it scraping the wear ring.

    Unless I have overlooked something my thinking is i need a bigger jet drive so i have finally managed to get hold of a Hamilton 771 which at first glance looks like it should run rings round the PP, the intake scoop is considerably wider and longer same for the duct leading into the impeller. apart from the major surgery to the boat to install the Hamilton is there anything i should be aware of? it looks as though i will need to move the engine at least 12" to 15" forward which means losing the rear passenger seat, but i think moving the weight further forward will improve the trim. The sturn always sits low in the water so much so the exhausts are below the waterline, not good for the engine when its stopped and makes it more difficult to clime onto a plane because the bow is up in the air. Also it seemed like a bad idea having water going up the control cables leading to annual replacement from corrosion. I look forward to hearing your views, is this a wise course of action? Before i start work on the conversion this winter. Mike
     
  2. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Hi Mike and welcome to our forum.

    Your problem is a far too small jet. Even with the original 140 hp or so, it is on its design limit, both in terms of power and rpms. Your engine mods didn't make life easier for it...

    Now the alternative: the Hamilton 771 has a 190 mm impeller and is limited to 130 hp/5000 rpm; it won't work either. But the 770-series can be stacked, and for you the 2-stage 772 might work quite fine. If you can get your hands on a really good (note corrosion and general wear) 771 for decent money, it might be possible to find 772 spares to rebuild it. A "copy" was produced in the US under the name of "Turbodrive" pre 1989. Also produced by "KEM Equipment, Oregon" under the name of "Kodiak".

    Better still would be a Hamilton 221. It is a newer design, with a variety of impellers and parts available. But note that, contrary to common belief, jets do not like high rpms; I'd say that to get a working combination, you should aim at about 5000 rpms at max power; better less than more.
     
    Last edited: Aug 29, 2018
  3. Michael Denner
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Calne

    Michael Denner New Member

    Hi Baeckmo,


    Thank you for replying, you confirmed my suspicions so a bigger jet is the way to go, the 771 is in very good condition for its age, original paint with Hamilton 770 logo printed in colour on the reversing bucket, a bit faded and a few minor spots of aluminium oxide showing through the paint its obviously spent most of its life out of the water. I picked it up from ebay for £700. Before i bought it i got in touch with Hamilton UK and apparently pretty much everything is still available for it, impellers £450 , wear rings, seals, bearings etc I wonder if that would extend to a longer shaft and second impeller casing to make it into a 772, or push the boat out and turn it into a 773 so i could put it on a bigger boat in the future, defo worth asking. At the time I enquired about spares I got a quote for the HJ213 as that looked like the jet i need but the cost is an eye watering £8471 plus vat! How can they justify that kind of price? its nowhere near the complexity or precision engineering that goes into making an engine. That was what made me grab the 771 while it was available. Although the service manual says its limit is 130BHP comparing it to the PP65 it looks like it should easily handle 200bhp. but i guess that’s because it does when its loaded with two or three impellers. Do you think it will cavitate in the same way as the pp if i open the engine up or do you think it will work better?.
     
  4. Michael Denner
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Calne

    Michael Denner New Member

    Another aspect that made me go for it was that the 770 service manual quotes the 771 having better performance than my boat when fitted to a boat with a displacement of 2 tons whereas mine is prob only 750 kilos so it must be developing considerably more thrust than the PP for a given input power. Is this the case or is a longer but heaver boat easier to get onto a plane?
     
  5. baeckmo
    Joined: Jun 2009
    Posts: 1,116
    Likes: 116, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    With the effort needed to convert the boat to another jet, it would be stupid to fit the 771, considering its design limits; it is a nono! But since you already got the 771 unit, collect the bits to upgrading to a 772, then you will have a suitable setup.

    I would not consider rebuilding to a 773 version; better to find a suitable jet for future boats, than fiddling with with something that "may or may not fit".

    On the hull/length/weight issue, there is one parameter which is paramount for the jet performance envelope; the slenderness ratio. It is calculated as: (waterline length)/(displacement volume)^(1/3). Low slenderness (ie short and heavy) hulls have very high resistance in the pre-planing speed range, often higher than at high speed. With too small "swallowing capacity", the jet will loose thrust due to cavitation when trying to get over the resistance "hump".

    The power density in the jet impeller is extremely high; you are asking a small rotor of less than five kg weight to transfer the output from a 400 kg engine with trillions of rotating, vibrating and jumping-up-and-down paraphernalia. There are simply limits to what can be done, even if vortex motion is one of the most energy-dense phenomena in nature! So; If it is worth doing, it is worth doing well......!
     

  6. Michael Denner
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Calne

    Michael Denner New Member

    Thanks for your advice, I’ll fit the 771 its got to work better than the PP currently does in my boat according to the formulas in the 770 workshop manual. And I will keep an eye open to obtain the bits to upgrade it to a 772. The engine weighs in at 170kg so it has excellent power to weight ratio. I'll keep you posted on any progress.
     
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