Outboard height

[Fab1]

I may be wrong but it's my understanding that the cavitation plate should be level with the bottom of the hull?

  It's just dawned on me mines lower than the hull by 3 inches.

Should I raise my outboard? I would of thought the dills would of mounted it correctly.

[noelm]

Yep, needs raising considerably, that foil will be dragging under water, making matters worse, that almost looks like a long shaft on a short shaft transom. That said, sometimes tinnies have a little "keel" that can create problems, depending on the HP, you might be able to just clamp it on with the screw gizmos for testing.

Edited February 3, 2022 by noelm

[noelm]

Depending on how it's mounted, you might be able to lift is up to the last holes to see how it goes? Too low can cause, high bow rise on take off, and way too much drag, causing low top speed and more fuel use, deeper draft making shallow water grounding possible, maybe that foil was fitted because of bow rise? Before doing anything, take it for a run and look over the back at the cav plate/foil when on the plane, it should be skimming the surface, not under it!

Edited February 3, 2022 by noelm

[XD351]

If your boat was a barge and never going to get near up on the plane it would be fine but in your case as Noelm has stated it is too low . I would love to know how it got mounted that low ! I do hope moving it doesn’t turn into a major mission !

Edited February 3, 2022 by XD351
To kill the evil that spellcheck is 😈

[Fab1]

I'm kicking myself not checking when I bought the bloody thing brand new!!!! I was looking at boating stuff and it dawned in me to check to only find out now after bloody 11 yrs.So annoyed.

To lift the outboard the existing mounting holes can't be used and the outboard clamps will be higher than the existing transom too.

 I'll rack my brain and see what I can do but i don't have any welding gear for aluminium or many tools now .

[noelm]

Measure from the top "lip" where the motor sits on the transom (in the centre) straight down to the bottom of the boat, it should measure 15" or 20" , then measure the little flat bit on the motor that sits on the transom to the cav plate, it should also measure either 15" or 20" and both boat and transom should measure the same, or very close anyway.

[noelm]

Can you take a picture from behind the boat looking at the motor and stern from about level with the motor, not from above because it distorts the angles.

[Fab1]

3 minutes ago, noelm said:

Measure from the top "lip" where the motor sits on the transom (in the centre) straight down to the bottom of the boat, it should measure 15" or 20" , then measure the little flat bit on the motor that sits on the transom to the cav plate, it should also measure either 15" or 20" and both boat and transom should measure the same, or very close anyway.

19 inches to hull or 19.5 to bottom of centre planning streak for transom height.

Transom to cav plate 22.5 inches.

That's where I'm getting my 3 inch difference.Should be 3.5 inch.

[Fab1]

19 minutes ago, XD351 said:

If your boat was a barge and never going to get near up on the plane it would be fine but in your case as Noelm has stated it is too low . I would love to know how it got mounted that low ! I do hope moving it doesn’t turn into a major mission !

You and me both mate.It got mounted that low from imbecilles not doing their job properly.

[Fab1]

7 minutes ago, noelm said:

Can you take a picture from behind the boat looking at the motor and stern from about level with the motor, not from above because it distorts the angles.

She's low mate.

[noelm]

Yep, that's low, now can you take one just a bit higher up so we can see the motor mount and transom? it doesn't look low enough to be a long shaft on a short shaft transom, but it's quite low and raising it will make a big difference.

[Fab1]

41 minutes ago, noelm said:

Depending on how it's mounted, you might be able to lift is up to the last holes to see how it goes? Too low can cause, high bow rise on take off, and way too much drag, causing low top speed and more fuel use, deeper draft making shallow water grounding possible, maybe that foil was fitted because of bow rise? Before doing anything, take it for a run and look over the back at the cav plate/foil when on the plane, it should be skimming the surface, not under it!

I've only got 4 mounting holes.Its using 2 bolts through 2 of them now.If I raise the outboard the 3 inches A..The existing bolt holes can't be used and B....The bolt holes in outboard bracket line up with the top edge of transom.

Agree with what you say.I fitted the foil to get the bum up a slower speeds mainly as per suggestions from various people.Now that I think about it last time out I was taking a good chop on the port quarter at a 45 deg angle and she grabbed like the foil dug in and nearly through us out of the boat.I'm convinced the donk is way to low and now with the foil it's making the problem more noticeable due to the increase surface area as the foil is probably 4 or 5 times bigger than the cav plate and digs in like a shovel.

 Hope i

5 minutes ago, noelm said:

Yep, that's low, now can you take one just a bit higher up so we can see the motor mount and transom? it doesn't look low enough to be a long shaft on a short shaft transom, but it's quite low and raising it will make a big difference.

[Fab1]

Geez I feel like a bloody imbecille not checking when I bought the bloody thing.Could be worse I guess.

[noelm]

A foil fitted on a low motor can be very dangerous, they do exactly like you describe, dig in and kind of "flip" the boat into a turn almost! Is there a gap between the top on the transom and the lip of the motor? it's a bit hard to see there, you sure the transom measures 20" in the centre to the bottom of the hull? not doubting your measurements, just need to be 100% sure what we are dealing with.

[noelm]

Just enlarged the picture a bit, there appears to be some kind of spacer sitting on top of the transom that the motor is sitting on?

[Fab1]

4 minutes ago, noelm said:

A foil fitted on a low motor can be very dangerous, they do exactly like you describe, dig in and kind of "flip" the boat into a turn almost! Is there a gap between the top on the transom and the lip of the motor? it's a bit hard to see there, you sure the transom measures 20" in the centre to the bottom of the hull? not doubting your measurements, just need to be 100% sure what we are dealing with.

No gap.There's a 20mm spacer.

100% she measures 20 inches mate. 

She dug in and the back end slew sideways mate violently.

2 minutes ago, noelm said:

Just enlarged the picture a bit, there appears to be some kind of spacer sitting on top of the transom that the motor is sitting on?

There's a 20mm spacer already.

[Fab1]

Here's a pic noelm.

[noelm]

OK, a 20mm spacer, plus the approx 75mm (3") below the boat equals almost 5", the difference between long shaft and short shaft......can you put the tape beside the engine, hooked on to the transom top, not the spacer, that's been added by the dealer or someone.

[noelm]

How close are the screw clamps to the top of the transom, forget the spacer is even there for the time being.

[Fab1]

Noelm, a bloke I'm talking to is saying that because I have an aluminium boat with a keel(my keel is exactly 2 inches wide and tapers down to the planning strake) , that my cav plate/foil should be level or there abouts with that. He said only on a smooth hull the cavitation plate should be level with the hull.

So if he's theory is correct my cav plate sits 3 inches from bottom of hull(smooth part) and 1 inch from bottom of keel. 

 I told him that my cav plate is 1 inch below keel and he reckons it's perfect.

Your thoughts? Here's my keel.

 

[Fab1]

Just now, noelm said:

How close are the screw clamps to the top of the transom, forget the spacer is even there for the time being.

3 inches away.If I raise out board 3 inches without current spacer the centres of bolt holes would be level with edge of the top of the transom.

[noelm]

Not the bolts you can see, the screw handle things on the inside of the boat, I guess your motor has them? you know those little gizmos you screw in to clamp the motor on? As it stands, that spacer serves no purpose at all, its just pop riveted on to look good, there is no strength there, and it's not needed, leaving a gap there is exactly the same.

[Fab1]

6 minutes ago, noelm said:

OK, a 20mm spacer, plus the approx 75mm (3") below the boat equals almost 5", the difference between long shaft and short shaft......can you put the tape beside the engine, hooked on to the transom top, not the spacer, that's been added by the dealer or someone.

3 inches plus 20mm is not even 4 inches.25.4mm is 1 inch.

Confused where the 5 inches comes in.

From the top of transom(No spacer) to bottom of hull(Flat part)is 19 inches.

[noelm]

Sorry, motors are measured in 5" increments 15" short shaft, 20" standard long shaft, 25" extra long and 30" ultra long, why 5" is anyone's guess. Transom sure looks like a long shaft by the tape. You might have to just raise it so the bolts are at the minimum safe distance from the top and put up with it?

[Fab1]

2 minutes ago, noelm said:

Not the bolts you can see, the screw handle things on the inside of the boat, I guess your motor has them? you know those little gizmos you screw in to clamp the motor on? As it stands, that spacer serves no purpose at all, its just pop riveted on to look good, there is no strength there, and it's not needed, leaving a gap there is exactly the same.

1 and 1/4 inches from the centre of them to the top edge of transom.

If I lift outboard up 3 inches as it stands they will grip thin air.