Dad's Tinny

[Moonlighter]

The best thing to do with that set of foils would be to take them off! They will be creating massive drag if they are underwater and doing no good at all.

[McKnight]

Thanks for the advice, I think lifting it is the likely option. I have the sheet metal guy at work lined up to make a transom extension.

Unfortunately it doesn't get out much so testing a couple of different setups is a pain (easier than getting my project back in the water though, that's a whole other story).

[McKnight]

Just an update, with some pics and measurements, transom height is currently is 380mm (15in) and to the AV plate is 445mm. So as some of you mentioned it is a long shaft motor on a short shaft transom. Here are some pics. (note it is still at an incorrect trim angle). I believe the motor is a 90 model evinrude 8hp.









Edit: Any better

[ericcs]

pics aren't showing up!

[McKnight]

pics aren't showing up!

Did that fix it?

[Chimo]

Yes.

Need to lift the motor some 5 inches.

[McKnight]

Wouldn't 5 inches put the AV plate out of the water? Or does it need to go that high so it just skims the water?

[aussiebasser]

As I said earlier, short shaft is 15", long shaft is 20". You have to raise the transom 5". You have to do this in such a manner that it is solid enough so that the motor can't twist it. Welding is about the only way.

[aussiebasser]

Find a bit of stainless threaded rod the same size as the trim holes and pit it right through both sides with a nut on each end to solve the negative trim issue.

[The Woo]

Yes.

Need to lift the motor some 5 inches.

As I said earlier, short shaft is 15", long shaft is 20". You have to raise the transom 5". You have to do this in such a manner that it is solid enough so that the motor can't twist it. Welding is about the only way.

Lifting it 5 inches will see it far too high.
1" to 1.5" at the most judging by those pics. There is a keel there as well which will cause significant turbulence.
And yes, the trim is tucking the engine in, driving the bow down. Trim it out a hole or two.

[gofishin]

Lifting it 5 inches will see it far too high.
1" to 1.5" at the most judging by those pics. There is a keel there as well which will cause significant turbulence.
And yes, the trim is tucking the engine in, driving the bow down. Trim it out a hole or two.

Woo, pics are deceiving due to significant -ve trim. 1 to 1.5" would not be anywhere near enough, but yes, possibly 5" might be too much (due to the external keel).

McKnight, is that 380 to the very bottom of the external keel extrusion, or top of it (I.e. Bottom sheets)?

You need to temporarily prop the motor so that the A/V plate is parallel to the keel, then measure up from A/V plate to bottom, and top, of keel. The bottom measurement and 1/2 way between these two measurements is a good starting point for a transom extension. If it were my tinny I would also be doing a keel-cut, to get clear water to the prop & the motor as high as possible. Remember, it is easy to go up after an extension (chock etc), but painful ($) to go down!
Cheers
Brendon




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[stevej]

sell it and buy the correct shaft length
take those silly foils off, considering they are on backwards as well

boats dont go fast enough for the boat to be sitting on top of the water
it can roll up a inch or two higher the bottom of the boat

[Fed]

Looking closely at the pictures I think a short shaft could be too high.
Foil is around the right way.

I'd remove the foil & play with the trim before looking at raising the motor.

I have to say when the thread first started the picture fooled me too, at first glance it looks like it was taken from a standing up position & the foil did look backwards.
Aussiebasser was onto it.

[Noelm]

maybe, just for kicks, lift the motor up as high as you can, looks like you might get an inch or two? remove the foil, fix the trim, and take it for a run, will only take a bit of time, and cost nothing to do, and MIGHT just make it acceptable.

[McKnight]

Woo, pics are deceiving due to significant -ve trim. 1 to 1.5" would not be anywhere near enough, but yes, possibly 5" might be too much (due to the external keel).

McKnight, is that 380 to the very bottom of the external keel extrusion, or top of it (I.e. Bottom sheets)?

You need to temporarily prop the motor so that the A/V plate is parallel to the keel, then measure up from A/V plate to bottom, and top, of keel. The bottom measurement and 1/2 way between these two measurements is a good starting point for a transom extension. If it were my tinny I would also be doing a keel-cut, to get clear water to the prop & the motor as high as possible. Remember, it is easy to go up after an extension (chock etc), but painful ($) to go down!
Cheers
Brendon




Sent from my iPhone using Tapatalk

The 380mm is practically inline with the bottom of the bung, so no it is not to the external keel.

Yes the negative trim gives the illusion that they are on backwards but they are not. I did try and get him to take some wide angle photos for better perspective.

The plan of attack is next time I am up there we will sort the trim issue out and remove the foils. Then take it out for some testing, get a clearer idea of what is happening at the correct trim.

Then we will start by chocking it up two inches then an inch at a time if it doesn't seem high enough.