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Old 03 August 2018, 09:40   #71
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Jeez stop guessing!

From Bruce's figures:

Transom cut-out to bottom of V = 570mm.
Current leg length from anti-vent plate to saddle is 635mm.
Anti-vent plate is currently level with the bottom of the hull V.

So, 635 - 570 = 65mm. Therefore 65mm down is the lowest an engine can be mounted without transom modification.

An engine with a 'long' leg is 508mm from anti-vent plate to saddle.
Since the transom is 570 then 570 - 508 = 62mm. So 62mm, as near as damn it 2.5", is the lowest position the anti-vent plate can be if using a 'long' shaft motor.
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Old 03 August 2018, 09:54   #72
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Bruce, that's exactly as it should be and you're not going to get it better by changing shaft length.

These folks telling you to get a shorter shaft can't do their arithmetic.

Also, they don't seem to understand that keeping the props in the water as much as possible will give you best overall performance.

Watch this video and note that, with the exception of when the boat actually leaves the water completely because of its speed, the drive is low enough to to keep propelling the boat, even when the hull is out of the water. The requirement is that the section of the hull rear of the bow is the running surface and if possible the hull should run and land on that.



If you go the route of lifting the engine too far, which a shorter shaft will force you to do, when your hull leaves the water you will also loose forward drive and the hull will be dead stick until it lands and the prop has time to regrip the water. During this time you will be at the mercy of the hull angle and the type of wave it lands on - it is effectively out of your control during that time. This will give you a seriously uncomfortable ride in the Solent chop. On the same tack, a propeller which can run partially surfaced without loosing grip will also help considerably in keeping the drive on giving you best performance and best ride.

Since your boat is a rib, much of its safety relies on the bow being high giving you advanced handling in following seas and steep seas. Keeping your engine low, provided it's within an acceptable range, which your is, will give you the maximum leverage at the transom to lift the bow by applying throttle so enhancing your ability to keep making progress when others are struggling.

Stick with it and learn your new engine is my advice.

It's unfortunate that the clearance with your A-frame is a nuisance but that can be resolved. And if you resolve that, you still have the ability to lift the engine one more hole should you feel it's necessary.

Go and use it and enjoy your new power.

1) Set 1" above the hull it won't loose grip because that's where it should be.
and in fifty years of powerboating I've never found "loosing grip" to be an issue. Set it right and trim it right.

2) Race boats don't use standard underwater units. Their setup is completely irrelevant to a standard outboard rib.

3) You absolutely do not want to hold the bow high. Risk of catching wind under the hull, it will land hard on the aft section and risk of flipping the boat on a steep sided wave. (there's a good example of that happening to a lifeboat on youtube.)

4) Hitting the "A" frame is not an inconvenience. The engine is mounted too high. Why else would it hit the"A" frame?
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Old 03 August 2018, 10:19   #73
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1) Set 1" above the hull it won't loose grip because that's where it should be.
and in fifty years of powerboating I've never found "loosing grip" to be an issue. Set it right and trim it right.
Read the arithmetic. And loosing grip is a constant frustration in power boating hence all the talk about suitable propellers and engine heights!

Quote:
2) Race boats don't use standard underwater units. Their setup is completely irrelevant to a standard outboard rib.
Nope. I use exactly the same drive as the V24 in the video. Completely relevant to a rib.

Quote:
3) You absolutely do not want to hold the bow high. Risk of catching wind under the hull, it will land hard on the aft section and risk of flipping the boat on a steep sided wave.
There is always a ridiculously silly example to try and prove a point.
Look at the RIB at the head of your Ribnet screen, it's a good running RIB with the bow high and a surprisingly similar attitude to the V24s in the video and while it's obviously on smooth water, with a bit of luck it will keep that stance while travelling over waves.
Plainly there will come a point for any RIB where the waves are too big for it to keep running at speed and that is where the RIB excels and where a well rigged boat and good driving become the important factors.
Quote:
4) Hitting the "A" frame is not an inconvenience. The engine is mounted too high. Why else would it hit the"A" frame?
The engine is a different physical shape to its predecessor.
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Old 03 August 2018, 10:22   #74
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I'm beginning to wonder if JW was responsible for this, of course the engine is a different physical shape, the new XL shaft is far longer than the old, long, shaft Opti. Had it been a standard shaft Suzuki then the difference would not be that great.
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Old 03 August 2018, 10:24   #75
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Wake up and smell the coffee.......
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Old 03 August 2018, 10:26   #76
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What a lot of nonsense.....

Wrong engine end of discussion
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Whatever...
Not often I agree with Xk59D but on this occasion I 100% agree with him
1" up is where to start and the engine should be longshaft not extra long as supplied
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Old 03 August 2018, 10:39   #77
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I give up. The arithmetic is in front of you.

'there's none so blind as those who will not see'
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Old 03 August 2018, 11:41   #78
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Not wishing to disturb your bitch slapping contest, when a XL, L, standard etc. shaft engine is mounted on its nominally correct transom, would we expect it to be mounted on the middle holes on the transom bracket? I.e, is a longshaft a longshaft when measured from the centre of the bracket or top/bottom?
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Old 03 August 2018, 12:31   #79
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Bitch slap pmsl as they say
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Old 03 August 2018, 12:32   #80
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bitch slap pmsl as they say
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