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Old 13 November 2011, 01:40   #1
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Country: Australia
Town: Sydney
Boat name: Lunasea
Make: Ribtec 890SX
Length: 8m +
Engine: Yamaha ME 421STI x 2
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First ride in Ribtec 890SX

Finally finished getting it back together and took it for a 15 minute run in Botany Bay.

The photo is at our local boat ramp with Sydney Airport in the background.

With just two on board and one third fuel, the Yamaha diesels would jump to 4000rpm instantly. From memory that is redline, so we backed off to about 3200.

As there was hardly any weight in the boat, the nose is really light and the tail with twin diesels is really heavy. With any trim at all it just porpoised. Maybe we should try some different props. Currently we have the Hydradrive 21 pitch four bladers. They are quite a large diameter prop. The spline looks the same as the Mercury sterndrives and we have lots of props to suit, so may experiment.

Unfortunately the GPS hasn't been hooked up yet, so no speed updates. Will get it going before playing with props.
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Old 13 November 2011, 03:55   #2
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Make: Ross Smith Cobra
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Nice boat!
What about trying a bit of ballast in the bow?
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Old 13 November 2011, 06:15   #3
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Country: Australia
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Boat name: Lunasea
Make: Ribtec 890SX
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Ballast is exactly what it needs. As all the deck space is forward, anything we add from refreshments to passengers will add 'ballast'.
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Old 13 November 2011, 06:37   #4
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Install a fat friend up front!
Kidding aside, I've used bags of lead shot the bow locker. Worked well.
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Old 13 November 2011, 09:13   #5
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Cuppla slabs of tinnies should sort it out Botany Bay - ya taking me right back now......
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Old 13 November 2011, 14:42   #6
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Fit the proper Yamaha 21 three blade prop. I am not aware of a Yamaha four blade. Are you sure it is a Yamaha one? The correct prop will lift the transom. All Ribtec hulls like a lot of keel weight, preferable amidships. Too much weight in the bow and the hydrodynamics of the hull will result in it rising and not pushing the hump away from the centre of gravity. Trust me I have done a lot of miles in this hull. AlanP
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Old 13 November 2011, 15:12   #7
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Quote:
Originally Posted by Alan Priddy View Post
I have done a lot of miles in this hull.
Understatement of the year
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Old 13 November 2011, 15:16   #8
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Country: Australia
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Alan, I was too excited when I wrote the first post. Yes they are Yamaha 3 blade props. The prop shop that cleaned them up thinks they are the Hydradrive prop but they are not sure as the are quite rare here.

It gets to 4000 rpm so quickly it feels as if it could use more prop but I guess that is due to the light load. I am not used to the turbo diesel torque. I appreciate the advice, and I guess I will leave it alone.

Jizm, I don't have any fat friends, so will have to settle for quantity. We have a bikini shoot booked on board so they should do it. Will post photos if the photographer gives me some.

Courageous, you are also correct. This was the one and only time we went out with no liquid refreshments, it won't happen again.
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Old 19 November 2011, 15:13   #9
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Went for another ride but I was too excited to take photos.

3-4 foot chop in the Botany Bay and the boat felt fantastic. Will easily redline with 5 passengers on board and full fuel tanks.

Covers distance pretty quickly ay 3200 rpm.

There was a blanket of fog covering the heads extending into the ocean so couldn't go for an ocean run. Never seen this before, very unusual for these parts.

Even with the extra weight I still can't use any trim without porpoising.

The layout of the boat is such that there is a huge sundeck forward with an anchor locker and 2 small storage compartments forward. These compartments are covered by a sunbaking cushion. It is not somewhere someone would sit underway and not anywhere that we could add significant balast.

I guess the boat runs very well so I should probably leave it alone and just run with the legs trimmed in.

Any suggestions?
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