Porpoising Ski Supreme

Discussion in 'Powerboats' started by SABoater, Aug 2, 2006.

  1. SABoater
    Joined: Aug 2006
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    Location: Johannesburg, South Africa

    SABoater Junior Member

    Thanks for all the feedback. The Ski Supreme is very similar in design to all of the other competition boats.
    1. The problem starts at about 58km with everybody in the front - battery is already in front of the engine (I would expect that to be the CG of the boat) with nothing other than the built in fuel tank at the back.
    2. Whilst 58km/h is the expected top skiing speed of the boat, I would expect the boat to go safely/comfortably into the low 60s.
    3. As soon as the weather warms up a bit, I will put about 70kgs in the front to see the difference.
    4. A trim plate is presently being fabricated. I will initially extend the bottom (approximately 500mm wide and 600mm long) with the ability to trim down by about 5 degrees should it be required.
    5. No new boat - wife would have apaplexy!
    6. I have corresponded with the original builders who confirm that the prop is correct. I agree that the cupping on the prop could be causing an imposed load on the back of the boat equivalent to a couple of Kgs and this may be an alternative.
    Thanks for the advice. Wish the weather was warmer so that we could get to some footing and everything else as well.
     
  2. Wakeboarderwski
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    Location: Canada

    Wakeboarderwski Junior Member

    Hello SABoater
    I was wondering how you did with the trim plate. Did it help you out. I understand the speed you are having the problems at is 58 km/hour(36mph).
    I just bought a 1987 Ski Supreme and at 72km/h(45mph) on calm water, it will start to porpoise also. The last time I had it out on some choppy water I was able to reach 88km/h(55mph) and it road steady.
     
  3. robk
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    Location: San Diego

    robk Junior Member

    55mph for an 87'??? Do you have a 400 hp inboard or a barefoot boat? When I purchased my 19.5ft closed bow 98' Mastercraft new it would hit 42mph max (260hp).

    While the basic design of tournament ski boats has not changed much over the last 30 years there are many subtle changes to the hull design. It's very possible these older hulls are not built to go as fast as you have mentioned. The outboard barefoot models appaer to be very different hull designs and do very well over 40mph.
     
  4. Wakeboarderwski
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    Location: Canada

    Wakeboarderwski Junior Member


    Before I seen the 250 indmar, my friend told me this ski boat did 55mph. I didn't believe him, naaa it's lucky if it will see 45mph-it's a ski boat. I have driven boats that have reached 65mph and I am 100% positive that both gauges are correct at reading 55mph and am eating crow with my friend. I most likely will not see this again until I am positive that the stringers are in good enough shape before I let this thing loose again at full throttle. I have not been a friend of the Ford power since a 302H.O. roller cam, fuel injected engine ate it's camshaft. This Indmar 351 has torque and RPMs unmatched by the 302 and is almost making me a believer of Blue Ovals again. When the boat reached 50mph and had a steady ride, it had lots of room left on the throttle to easily reach 55mph. Until that point, I still would not believe that this boat would see anything over 45mph...but it can! I had another boat for 15 years that would gradually get up to 48mph, this boat rockets past that and that's by the seat of the pants not looking at the gauges. This engine would be loved by barefooters. Indmar has some tricks up it's sleeve with this engine they built. It also did very well on gas for the time spent skiing and tubing compared to the other boat I had. Lots of power and less throttle needed to do what was required of it.
     
  5. robk
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    robk Junior Member

    If you're running the 351 you should have tons of torque like you're saying. I was in a 92' Mastercraft with a 351. It had so much more power than my 305. Also too the older ski boats aren't very big. They sit very low to the water. All these factors could help you acheive that 50+ mark you are talking about.

    Sounds fun.
     
  6. Wakeboarderwski
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    Wakeboarderwski Junior Member

    I had white knucks on the steering and throttle hoping the choppy water wouldn't send it for a loop. The ski hull dosn't cut through the chop as nice as a V hull.
     
  7. robk
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    robk Junior Member

    You're in Canada. What's the water temp there? Do you have to wear a dry suit? Most of the water here is in the low 70's throughout the summer. At Clear Lake in Northern Ca this August I was registering 90degree water. I've done some dry suit runs in the winter with 55degree water.
     
  8. Wakeboarderwski
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    Wakeboarderwski Junior Member

    Today we are at 80f outside which is great for this time of year. The hottest summer day in Sask was 98. The water at it's warmest reaches 70 but the cooler nights bring it down fast in Sept. I would say it was 55 Sept 4th. No wet or dry suit. Ski on, rope out, jump for the handle and go. Everyone each says a few kind words when they hit the water but you do adjust eventually at 55f. No pain, no gain
     
  9. Paul Lastrucci
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    Location: Pretoria

    Paul Lastrucci Junior Member

    Greetings,

    I now have a 1987 Ski Supreme and my pal had a 1983, to me they feel like two different boats, I ran them side by side and the 87 porpoised a bit more in rough water but not uncomfortable. The hull changed in 87 being an all fibreglass no wood stringers with tracking strakes and spray rails on the edge of the hull at the bottom. It feels a lot tighter and tracks nice and straight. SA boater you are correct, they came stock with a 12X13 prop. The 83 we had a 13X13 and did not give the same tug on take off (Slalom) as did the the 12X13. They both run the 351 Windsor Sb Ford motor PCM (83) and Indmar (87) I have a spare 15 pitch prop for the 1" shaft, tried it on the 87, not a nice boat so kept the 12. I freshened up the motor on the 83 so it ran strong before it was sold. The 87 was a good find it only has 540 hrs total time and is immaculate

    We also had a 83 Ski Nautique 2001 with the barefoot option (454 Chevy Mercruiser 330 HP) and strangely enough the Ski Supreme feels much smoother. I visited Ski Nautique in Orlando Fla to get a manual to set up the boat as we had a bad vibration on the boat. I later found out that it hit something prior to our purchase and had bent the proshaft a bit. It must have been a quick repair job they just had the prop reworked and sold it to me as new. MMmmm I just did not have the time to get it on the river and check it out. Mistake!! I took out the shaft and had it straightened and what a difference. The big block had tremendous torque but was a gas hog and also porpoised a bit in rough water. The comp water ski boats of that era like smooth water period.

    What I like about these boats is that they are timeless I can't pay a Million Rand for one of the fancy new boats, it's a bit steep and for that price it should fly and make tea.

    Keep on boating

    Paul
     
  10. Wakeboarderwski
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    Wakeboarderwski Junior Member

    Hi Paul
    I have some questions for you on the 87 Ski Supreme.
    I was wondering if you know how the metal engine mounting plates are attached to the boat? Are they lagged into a wood beam behind the fiberglass subfloor or did they have a metal backing behind the fiberglass?
    On the 87, is the Indmar rated at 250HP?
    Does it have the metal stamped valve covers or raised(finned) valve covers. I am trying to find out if the 250HP Indmar I have is original or has the internals been altered. It pulls as if it's got 300 horses working for it.
    Thanks
    Mike
     
  11. Paul Lastrucci
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    Paul Lastrucci Junior Member

    Hi Mike,

    The stringers are steel and they are encapsulated with resin, and round about where the engine and the velvet drive mount on the stringers, there is a steel plate exposed longitudinally along the stringer about 1,5'. The Tennesee hull as it's sometimes referred to, came out of the "The New Supreme Industries, Inc" factory in Louisville TN when they were still around and certainly in my opinion, a vast improvement quality wise from the pre 87 boats having had both.

    Yep, mine is the 260 HP and it has the stock gold Indmar steel rocker covers, a 600cfm 4bbl side mount float Holley (4160) on an Edelbrock Torquer aluminium intake, and from my research appears to be original. It is also strong, fuel efficient and very reliable. I am skeptical to squeeze extra horsepower out of it with aftermarket bits as they tend to become a bit tempramental, it does not bode well when out with the friends and family and you're the only one fiddling and all they want to do is ski. There is a lot of hop up bits for the Windsor family of Fords however in the marine application up spec'ing the correct cam requires a bit of science. It's such a nice package in stock trim.

    Cheers
    Paul
     
  12. robk
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    robk Junior Member

    If you are used to a Chevy block and then have a 351 Windsor, it will feel like 300 horses even though it's rated at 250hp. You are just feeling the effects of having substantially more torque. While both Chevy and Ford make great V8's they rev completely different. Chevys are screamers and Fords are low end torque monsters.
     
  13. Wakeboarderwski
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    Wakeboarderwski Junior Member

    Thanks Paul for the best explanation of the 87 SS hull. No one has been able to answer this question before. Glad I don't have to check for rotten stringers. My 351 has alumimum raised valve covers, that's why I'm not sure what's lurking under them. May be only cosmetic.

    Thanks robk for tork curve info. What ever Indmar did putting the engine together, it worked, torky, smooth and fuel efficient also. The previous 77 351 Windsor came nowhere close to the 87 351 Windsor.
     

  14. Paul Lastrucci
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    Paul Lastrucci Junior Member

    That is so!

    However the BB Chevy is also a stomp puller! There appears to be significantly more marine performance bits available for them.

    Had some time with a 460 cu in Ford in a Jet boat (18' Kona hull, Berkeley 12 JC). We ran it at Cape St Francis up the Krom River here in South Africa with the jetovator set a bit up leaving a 50ft rooster tail. This river's level rely's on the tide and at low tide exposes a few sand banks, so an inboard prop boat is not an option if you want to play all day.

    In your neck of the woods, the 460's have a reputation amongst boaters of making huge bundles of torque, equally, are hugely popular amongst the So Cal "river runners."

    You may have seen what they are up to in New Zealand with 502 cu in Chevy's and jet drives, giving tourists wild rides up and down the rapids. If you think a Ski Supreme porpoises, -- The sound is awesome, -- the pilot is on and off the throttle all the time, oversteering to miss huge half submerged rocks all the way up and down the river, with about ten paxs holding on for dear life. Truly a wild ride.

    The BB Chevy, make no mistake is no slouch in the torque dept at all,-- nice thing is, they're also screamers! just like their little SB sisters.

    It's the old story:- "Horsepower is what you read about, torque is what you feel."

    Cheers
    Paul
    Sunny South Africa
     
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