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Old 27 July 2018, 16:00   #41
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Here you go.

Outboard Motor Shaft Length

Do you have your receipt handy or the serial number? Can figure it out with that probably.
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Old 28 July 2018, 01:21   #42
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Df150apx
(s/n 15003p-810670)
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Old 28 July 2018, 01:22   #43
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Thanks Neil & Xk59D and Beamish and others. On 3rd August will be at boatyard with camera, metre rule and tape measure and will report back
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Old 28 July 2018, 01:33   #44
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Originally Posted by brucehawsker View Post
Df150apx
(s/n 15003p-810670)


X is an extra long shaft
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Old 28 July 2018, 01:52   #45
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The new motor has a shaft length of 635mm, I guess your your optic may have been a 508mm.
Not sure any amount of measuring will help if this is the case.
Maybe best to talk to the company that did the work.
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Old 28 July 2018, 09:37   #46
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Bruce, the plate being referred to is the first one above the prop and its correct title is an anti-ventilation plate. Folks, wrongly refer to it as an anti-cavitation plate and then shorten that to cav plate so making it more confusing. Its purpose is to prevent air being drawn down into the propeller blades.

From your last picture, the plate looks to be about level with the bottom of the V of your hull. If this is the case, the engine should perform satisfactory. For general use, 25mm (1 inch) below the bottom of the V to 25mm above the V is a good range to be within.

There is a tendency for folk to mount outboard engines too high to achieve absolute maximum speed but it will always come with disadvantages. Primarily, ventilation in turns, poor grip in rough seas, poorer grip when the boat is heavily loaded and a markedly harsher ride when wave hopping.

You may well find that some part of the new engine is inconveniently splashing water, that's just hard luck really but you might eliminate it and still have your engine within range by adjusting the engine height up or down to either lift the offending part out of the water or lowering it to bury the offending part deeper into the water.

Do you mean the boat is lower in the water when at rest? If so, the new engine must be heavier than your Opti and you're stuck with that. If you mean the boat is travelling more bow up and so lower in the stern then the Suzuki prop is said to be 'bow lifting'. What it's actually doing is pulling the stern down. Generally this is considered to be a desirable trait because the prop is more capable of gripping the water in adverse conditions and it also assist in lifting the bow when applying throttle in following seas. However, it also makes climbing over the hump to get on plane more difficult. As you suggest, trim tabs will be a remedy for that. They will allow you to balance the boat fore and aft and will also allow you to counter listing so preventing slamming in rough conditions.

Let us know how you get on with it.
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Old 28 July 2018, 12:09   #47
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<<<There is a tendency for folk to mount outboard engines too high to achieve absolute maximum speed but it will always come with disadvantages. Primarily, ventilation in turns, poor grip in rough seas, poorer grip when the boat is heavily loaded and a markedly harsher ride when wave hopping.>>>
One inch above the keel line is not "too high" and unless you have a very badly designed boat, it's not going to "ventilate in turns" have "poor grip" or give a "harsher ride when "wave hoping" set one inch up. If anything the opposite. Lowering the bow when "wave hopping" presents the finer entry closer to the bow keeping the boat more level and reduces "slamming". A deep set prop will raise the bow and make this worse.
As Beamishkin say's, one inch above is the "starting point" and if max speed is the only criteria you're interested in you'll end up well above that.

Set 1" above keel..... From about two minutes fifty on....




His engine is hitting the "A" frame when it's tilted! It is already visibly set too high on the transom and with his anti-ventilation plate (Cav plate) set below the keel it's too low......Sorry, this boat has been fitted with the wrong engine.
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Old 28 July 2018, 12:29   #48
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One inch above the keel line is not "too high" and unless you have a very badly designed boat, it's not going to "ventilate in turns" have "poor grip" or give a "harsher ride when "wave hoping" set one inch up. If anything the opposite. Lowering the bow when "wave hopping" presents the finer entry closer to the bow keeping the boat more level and reduces "slamming". A deep set prop will raise the bow and make this worse.
As Beamishkin say's, one inch above is the "starting point" and if max speed is the only criteria you're interested in you'll end up well above that.

Set 1" above keel..... From about two minutes fifty on....




His engine is hitting the "A" frame when it's tilted! It is already visibly set too high on the transom and with his anti-ventilation plate (Cav plate) set below the keel it's too low......Sorry, this boat has been fitted with the wrong engine.
Perhaps you need to untwist your knickers and read my post again.
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Old 28 July 2018, 12:54   #49
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Perhaps you need to untwist your knickers and read my post again.
Maybe you need to look at the photos again and check where his tilt tube is sitting with each of the engines.

50MPH is a reasonable expectation from this outfit and for that the cav plate (sorry anti-ventilation plate, not wanting to cause untold confusion) is too deep. The transom assembly is too high...his engine's hitting the "A" frame when it's tilted.
Join up the dots..............
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Old 28 July 2018, 14:59   #50
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Perhaps you need to untwist your knickers and read my post again.
Last tango is exactly right
The ops origional post suggested he had an idea something was amis fitting trim tabs is covering up a fault and introducing another.
Running with tabs all the time is like running with the handbrake half on
To get the best out of the boat and engine the answer is get the set up cottect from the outset
You would only run 1" down on a heavy underpowered plodder slow boat not a 40kt+ high performance rib
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