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Old 17 October 2017, 22:15   #1
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Country: Canada
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Am I exagerating or this engine is still too low?

hey guys, first I have to say that I really appreciate the discussions and opinions on this forum. I've been a long time reader, not so much of a contributor, but I learned a bunch on ribbing from you.

A couple of weeks ago I decide to bite the bullet and lift up my engine to the fourth hole (highest setting). I did it in order to improve the general handling, to increase wot speed and most importantly to reduce porpoising at high speed (mostly when I'm alone in the boat)!

After a run on the river I can say that the behavior at WOT has improved a lot even if, in my own opinion, there is still a lot of water splashing over the anti-ventilation plate.

The problem is now that at cruise speed the boat purpoise a lot more than before. I tried different weight distribution (more weight at the front or at the back) but to no success.

Tech Spec:
4.5m see picture below...
40 hp Evinrude Etec (tiller)
15" pitch propeller (solas amita 3?)
cruise: 3500 RPM, 31 km/h
wot: 5460 RPM, 49 km/h

Sorry for the poor quality of the video, I was alone. Also I shouldn't have enabled the auto-stabilisation of the image in youtube as the engine looks like it's moving all around like it wasn't correctly fixed to the transom but that's just visual artefact of the stabilization...
I've put the entire video here: WOT / correctly trimmed is @ approx 1:15

https://youtu.be/MupKH9528iU

Here's a picture of the engine height in relation to the boat:

As I can't increase the height of the engine anymore, I was thinking about buying a fix set back/ jack plate like this one: Hi-Jackerô Fixed Jack Plate 4 inch | T-H Marine Supplies

It would allow me to increase the engine even more and maybe get the engine running in "cleaner" water because of the 4" set back.
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Old 18 October 2017, 01:07   #2
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wouldn't go any higher than that also is it just the pic but your outboard doesent look as if its tilted all the way down
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Old 18 October 2017, 02:08   #3
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Plus 1 on not down.
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Old 18 October 2017, 03:18   #4
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Country: Ireland
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I would check the specs for wot for that engine as it would appear to me that you are not within the specs for the i2 etec. I think you should be achiving circa 5750 rpm at wot. I do agree that the engine height looks right. Tsm
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Old 18 October 2017, 08:11   #5
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You've not got a lot of weight up near the bow?

The porpoising starts when the leading edge of the whetted surface falls behind the centre of gravity of the boat and it's relying solely on the prop thrust to keep the bow in the air. Moving weight aft can help. (and check the engine's trimming down all the way)
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Old 18 October 2017, 11:03   #6
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Iíll post a new picture tonight with engine trim all the way down. engine is trim to Ďneutralí position On previous picture.

For the weight, I guess youíre right Ďlast tangoí. I tried to move as much weight as possible towards the front. but still itís a tiller boat so I have to seat in the back. 12g Fuel, batteries and seat in the middle (a bit towards bow). Anchor and safety kit in the bow locker.
I guess I will have to bring someone with me to seat in the front to counter balance my weight! :-)
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Old 18 October 2017, 14:03   #7
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Quote:
Originally Posted by savard02 View Post
I’ll post a new picture tonight with engine trim all the way down. engine is trim to ‘neutral’ position On previous picture.

For the weight, I guess you’re right ‘last tango’. I tried to move as much weight as possible towards the front. but still it’s a tiller boat so I have to seat in the back. 12g Fuel, batteries and seat in the middle (a bit towards bow). Anchor and safety kit in the bow locker.
I guess I will have to bring someone with me to seat in the front to counter balance my weight! :-)
Sorry.
I meant to move weight back to stop porpoising. You want to get the centre of gravity behind the leading edge of the whetted area.
Too much weight forward will cause the problem
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Old 18 October 2017, 17:32   #8
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Quote:
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Sorry.
I meant to move weight back to stop porpoising. You want to get the centre of gravity behind the leading edge of the whetted area.
Too much weight forward will cause the problem

You originally said Aft which is back. Did you mean to say forward ?
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Old 19 October 2017, 03:39   #9
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You originally said Aft which is back. Did you mean to say forward ?
No I meant "aft". I think the OP misunderstood.
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Old 19 October 2017, 03:50   #10
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No I meant "aft". I think the OP misunderstood.

But to help porpoising I think you need to move weight forward surely
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