1984 Evinrude 25hp mounting

[shimanok2]

Hi all,

I have been fixing up the subject outboard (with help from this site) as well as a 1981 Mirrocraft 14'. I got the long shaft motor for pretty cheap so when I was replacing the transom on the boat I updated it from 15 --> 20". Well apparently it should be 22" because my cavitation plate is currently sitting ~2.5" below the bottom of the boat. I've read a jack plate will solve this but they're rather $$$. Can I not just make a spacer to raise the outboard up and then bolt it through the transom? Or would a jack plate be a better option and why? The transom itself is 2 sheets of marine ply, glued and screwed, then stained and sealed with numerous coats of the Old Timers Formula. All holes were over-drilled, epoxy filled and then re-drilled appropriately. I wouldn't be able to do this same amount of prevention in drilling thru the transom as-is, but would do my best to seal it up tight with marine sealant.

Thanks again for the support!

 

[shimanok2]

I didn't see a way to edit so will add another post.

Edit: I did have the boat out yesterday and there was water spray coming over the transom so I do think the motor needs raising. The boat was pulling left too some but I didn't see any trim tab. Seems that wasn't a feature on this years model. I assume if after the height is corrected and it still pulls I'll need something like a torque tab to correct this.

 

[racerone]

Put a 1" spacer on top of transom and test run----Then put bolts through the transom.----Holes for that are already there.

 

[shimanok2]

I've mostly seen that the Cav plate should be flush to 1" below the bottom of the boat. Should I not just target this right from the start with a 2" spacer?

Even with a 1" spacer, I won't be able to clamp the motor down well for trials, so I'd like to get this as close to correct as possible the first time.

 

[racerone]

Do what you feel you have to do .

 

[shimanok2]

Thanks racerone. I ripper a rough cut block down to 2x2" to match the transom. Cav plate is about 3/4" lower than the bottom now. I don't think it can be tested as is so I'll just mark it and start drilling.

 

[909]

Good job on raising the cav plate, but don't you feel your clamps are a bit high. It's barely on your transom.

 

[jimmbo]

Keep in mind, that your boat has pronounced Keel, and even though it does end a bit in front of the transom, there can still be turbulent water behind it. You might have to drop down a bit. One other caution, you might find the engine inside the boat with you, with that method of securing it it

 

[oldboat1]

After lake test establishes height, run a couple of bolts through the engine mount from the outside.

 

[flyingscott]

looks like the first time in reverse your motor will be leaving you. buy a proper transom extender or mount it better.

 

[clemsonfor]

I was thinking that his pictures were just for mockup. And he was going to do something more permanent and secure. At least that's my take and what I thought he had planned!

 

[shimanok2]

Apologies, I'm apparently not getting email notifications of activity.

I was planning on keeping the wood block there (after it's sealed), and run a plate (Think I've got some 3/16" SS) on the inside and outside covering the top of the transom and the support block. I'll also have a piece of 3/8" flat stock on the inside below the transom cap to fill that gap. Some 5/16" SS bolts will run through all of it. You don't think this will be enough? This seems to be the same concept as an actual transom extender.

 

[jimmbo]

Your Strap across the Clamp Screws is placing a Rotational Force on the Transom, and the block of Wood is the Bearing-Pivot Point. Set the Lock/Release Lever to Lock, Grab the Gearcase, and Yank away from the boat and see if it remains on the transom

I wouldn't trust it at Trolling Speeds, let alone WOT

 

[shimanok2]

Yes, the strap was only temporary as I'm doing this by myself and can't hold, adjust and take measurements at the same time. I don't see why what I described in post 12 won't work. It's the same concept as a transom extender, just beefed up.

Edit: Meant to include that if I lowered the motor down to where the clamps would sit below the interior lip of the transom cap, the Cav plate would be ~2" below the bottom of the boat. This is based on using a straight 2x flush with the bottom. It's ~2.5-2.75" below with the motor bracket sitting flush on the transom, so I don't think this will offer much benefit raising it only 0.5 - 0.75".

 

[tphoyt]

I once made an adjustable bracket to solve this problem. Unfortunately I sold the boat and don’t have any pics but it was made from 3/8’s aluminum angle. It raised the motor 5” and held it off the transom 4”.
Worked great. At the end of the day it still cost me over $100 to make it with all stainless bolts.

 

[shimanok2]

I thought about doing this as well but then saw some talk about jack plates. So far I haven't invested a lot into this setup so but this seems important (Ha) so I ended up ordering a TH Mini Jacker plate. This should solve my problem although will put more holes in the transom. Oh well.

Next question, I see this jack plate is adjustable in the sense it can be removed and raised or lowered to the next set of holes which are 1" apart. So where should I target the Cav. plate to be then? Even? 1/2" down? I saw a lot of comments from folks using the mini jacker to raise their motors up so the Cav plate was an inch or two above the keel. They were doing this for running in super shallow water though and this doesn't apply to me.

Also, this model has 4" of setback. Does this change the height at which the Cav plate should be?

Thanks again for all the advice!

 

[tphoyt]

Personally I would go with the same plane as your hull. You can always adjust up or down if you feel you need to.
The 4” set back shouldn’t have any effect on the height. I feel like you made a great decision by doing this. Now you don’t have to wonder what’s going to happen.
Best

 

[shimanok2]

The jack plate is due in Friday. Hope to have it installed and sealed up that night so I can test it Saturday or Sunday. I'll report back then.

Thanks again!

 

[jimmbo]

A 4" Setback is minimal, but you probably could raise the engine an extra 1/4" higher, not that it would really matter. Raising the mounting height of an engine doesn't really offer any speed/handling improvements until 45+mph

 

[shimanok2]

Got the boat out for a test run yesterday and it performed much better than the initial trial. No water spray at the stern and got up onto plane quicker. One thing I did notice though was that once on plane if I gave it a lot of throttle the engine speed increased but it didn't seem to pickup speed at the same rate. This didn't appear to happen if I slowly increased the throttle. I've read this could be a spun prop hub. Could it also be pitch related? Of course I had my cheapo tachometer hooked up but forgot to look at it. No way I could have tested WOT though as there was some decent chop. I could hear and feel the RPMs change when I tried, I assume the prop getting some air.

I've attached a picture of the lower unit while on plane and the prop. Is the Cav plate supposed to visible? The Prop is clearly a Michigan but there's 2 engravings and they overlap, of course in opposite directions. Seems to me CCW is "MICHIGAN 012639" and CW is "HH136858". Neither of these mean anything to google though. I may stop at a local marina to see if they can decipher. Would contacting Michigan be worth it? If it is a spun hub I'm hoping the new props come with them as that part through BRP is discontinued and I don't see any on ebay.