bertram31.com

Any outboard experts out there?

Yesterday was a big day at the boat shed as I mounted the engine! Now it's time to second guess my engineering of the mounting height.

1963 Bertram 25
24 deg deadrise
10" Bob's jackplate
30" shaft G2

As shown in the photos, the engine is mounted as low as possible without using the "optional" top hole on the G2 transom bracket. The engine is fully trimmed in. The pivot pin of the engine is approximately to 24" off the transom, and the extreme edge of the anti-cavitation plate is 47" off the transom. The plate is approximately 2" above the bottom of the boat, as measured with a straight edge.

Too high? Too low? Just about right? Rigging manual is silent on this subject (with good reason!)

https://www.amazon.com/photos/shared/7O ... sN9fdrLVft

Thanks!
Cam

Cam,

based upon my research you are pretty close, maybe 1/4-1/2" too high. I'd roll with it and see how it does, the best part is that you have another hole on the outboard so no matter what it will work.

Standard install without a bracket the anti-ventilation plate should be 1/4" below the bottom of the hull

folks that do brackets state every 12" back you can go up one inch. If you are 22" back I'd think that would be just under 2" more specifically 1/6 of an inch under 2"

so adding it up, 1/4" under for stock and you are 2" above and should be a little less than 2" I'd say you are .25 + .166 = .4166 or a little over 3/8"

I just re-read your post, you have a bob's jackplate. how much travel does that have? can it go both up and down?

If it will only go up, I'd mount the engine as low as it could go and then fine tune to the correct height via the jackplate.

Cam,

Any meter tape that doesn't have metric as primary and perhaps (remotely) inches as secondary, cannot be read by 96% of the population on planet earth.

Second, isn't all this metal frame a bit flimsy? OK it has the right bolts etc, but isn't it a bit too flimsy for such a big motor?

I may be wrong, I wish I'm wrong.

without a bracket the cav plate should be even with the bottom of the hull
there is a formula somewhere online for set back and cav plate height so it might be ok ill look for the formula

See if this helps for info/.

https://www.boats.com/how-to/the-outboa ... justments/

ktm_2000 wrote:I just re-read your post, you have a bob's jackplate. how much travel does that have? can it go both up and down?

If it will only go up, I'd mount the engine as low as it could go and then fine tune to the correct height via the jackplate.

Jackplate is all the way down now. It has about 7 inches of travel. I'm not sure I'm measuring the height at the right spot. The guys on the Evinrude board have said to measure at the leading edge of the prop. If that is correct, I'm close to 2 inches low. I'll mount the prop and re-measure. I'd like the jackplate bottomed out and the engine at a good height when launching, and bump it up when she is on plane. It's an experiment. I'm not sure anyone has ever done this to a B25!!

Yannis - here in 'Merica we use inches, damn it!! We keep expecting the rest of the world to catch on!! That bracket is rated for over 400 horse-power. I'm not sure how many kilowatts that equates to, but she is one stout piece of aluminum!

Thanks, Bruce!

Thanks
Cam

Cam, no mater what, I wish you all the best of luck and enjoyment of your Bert.

Between what I've read and what Bruce has posted, It seems there is a lot of flexibility in how high to mount. You've put yourself in a great position with the jackplate and its 7" of travel.

I'm guessing with the jackplate you could adjust the height fairly easily with some wrenches.

I would start the whole thing off with the motor mounted as low as possible and figure out what you like by testing

That was the concept...adjustability. The jackplate is actually hydraulic, controlled from the helm.

It's an experiment!

Cam, one thing to consider is how the boat will perform at low speed. Do you know what its attitude will be at rest (chines under or ???)? We had a bracketed motor on a shorter deep V hull and its performance at idle or trolling speeds was unacceptable, it hunted and wandered as if we had been feeding it Whiskey!

With your jack plate being hydraulic, you may find that you want to raise or lower the motor at low speed to improve performance and that may change which end of the range you want to set your ideal planing height to.

Also, think about the tilt/trim at rest to ensure the lower unit can be fully out of the water when the boat is moored or docked.

I am so excited for you, getting closer by the minute!!

sorry for the slight derail - I am thinking about the possibility of a similar jackplate and not doing a motor well on my project.

in looking at the pics from the profile perspective, it seems that the combination of the 10" of setback + the lift, they both might be enough to allow tilting the motor up so as the skeg would be out of the water.

I doubt that it would fully replace having a motor well as it is probably not enough to fully tilt the motor, but the question is if it would be enough to clear the water line and make it possible to clear debris from the prop.

When you get power to the jackplate and motor, could you extend the jackplate to the highest point and then tilt the motor for a Pic?

I couldn't make that work without extending the setback. The water line is a long way up from the keel, and you'll want a 30" shaft engine. Soren over in Denmark used a Port-a-Bracket which has more setback and much more lift. Here are a few pictures I saved from the old days of the B25 board:

https://www.amazon.com/photos/shared/CB ... Gvs-UmZn-w

That's a bolt on, no cut solution, and much quicker and easier than the path I started down. I may name my boat "Put Down the Sawzall". That tool has resulted in lots and lots of work!

Cam, might as well throw my $0.02 in. I think you are too high--I would drop down that motor down one more hole which is about 3/4". Here is why--

The starting point for me has always been go from the bottom of the hull with a straightedge to bottom of anti-ventilation plate (motor level) with no setback. Then on a higher speed boat the 1" per 12" of setback works. However since this is a deep vee single engine and not really a high speed boat (Baron not withstanding) I would be a little more conservative and probably just run about 1/2" or so per 12". Two reason; 1) you want the prop down low for the hole shot where you can get plenty of clean water to get up on plane (the boat will pivot on the transom and the lever effect as the bow drops down will tend to pull the prop out of the water because it is 3' behind the transom); and 2) with the deep vee you when you heel in a turn it may pull the prop up to the point it ventilates. Not a big deal just back off the throttle until it hooks back up.

But since you have a jack plate even if you are too low it is a simple matter to trim it up the ¾ inch or so. I have had a Bob’s Jackplate for about 15 years on my daily driver, a 250 hp 21' center console and it becomes second nature after a while to tweak the trim and Jackplate while keeping your eye on the water pressure gauge. Jackplates are really transformative.

PS what kind of prop and pitch are you planning to run--props make a huge difference in the performance. What is the gearset ratio on your motor?

Todd,

You are probably correct. The idea was to keep it low to get out of the hole and then use the jackplate lift to trim it on plane. Your 1/2" per 12" ratio (13 mm per 305 mm for Yannis ) is about where she sits now if measured from the leading edge of the prop. I've never used a jackplate, so I'm on the steep part of the learning curve.

The G2 has a 1.85:1 gear ratio, 5400 - 6000 rpm. The prop I have is a RX4, 4 blade, 15"x 16"pitch. I made that choice based on feedback from an owner of a Grady-White that is about the same size/mass of my B25:

"My G2 300 spins an RX4-16 WOT at 5750 on my boat (5500 dry, 9'6" beam, 23' + 3' bracket)."

Thanks for your input.
Cam

Cam, Just thinking about you prop selection.
That is a big torquey motor and I am wondering if you are a little underpropped with a 16". Should be a hell of a hole shot with a 16".
Plug in your specs with about a 10% slip factor here: http://www.mercuryracing.com/prop-slip-calculator/
Of course it depends on how you use the boat--if heavily loaded in rough conditions then a little more low range is good. If on the other hand you are a haul ass kind of guy –then prop for speed. I certainly hear good things about the RX4. Did you buy it through one of the try it out/ exchange dealers?

Quite possible. I am at the extreme low end of the pitch range. Well see what happens in the water. The deal for the engine included all new rigging and new prop.

I was able to connect a battery to the engine and use the cowling mounted tilt/trim controls to move the engine. It's alive, Dr. Frankenstien!!

The engine must be tilt limited by the previous owner because it can tilt almost to horizontal. I'll need to connect all the rigging to adjust this.

https://www.amazon.com/photos/shared/7G ... PGwDXc_9Ed

Cam, beautiful to the ej point!

When does it get warm enough for boating down your way? I'll bet you can't wait.

the end is near, can't wait to see this rig on the water.

Cam
Looks great. Little off topic , what color is that blue. I love it, would like to do mine that color someday.
Maybe if my ship comes in.

Thanks! The end is getting closer...maybe not near. I'm still averaging about one or two days a month at the boat shed. It'll happen...might not have any upholstery or pipe work...but I intend to get some use out of this boat soon!

Hull is Awlcraft 2000 Bahama Blue, Oyster White topsides.

Cam

Cam, I'm getting ready to pull the trigger on a Bob's jackplate. What do you think of the powder coating on it, is it worth the extra increase in price

Did you do anything special in preparing the glass on the outside of the transom to take the extra load of the bob?

The reason why I ask is that I am going to fill in the I/O holes with 4-5 layers of 1708 sat morning then was planning on adding 2 layers of 1708 over the entire bump-out Sunday. The area will then be faired and gelcoated. Any suggestions?

Welcome to the darker side...outboard and a jackplate! You are downright crazy, man!

Powder coating looks good, but unlike chrome on your engine, it has no performance advantage!

I wouldn't add more glass to the outside of the transom as it will be a PITA to fair with no benefit. Taper grind the I/O holes to a shallow angle so you get significant overlap between new glass and old glass when you fill the shallow holes. Might require more than 4 or 5 layers, but I don't remember how how thick the outer glass is.

If you want to add more strength to the assembly or to distribute the loads over a wider area, work on the inside. I glassed in a 1/4" aluminum bar in the plane formed by the jackplate's top mounting holes. Serves as a gigantic washer.

A couple of notes:
- I made a plywood template of the jackplate mounting surface/holes to have something light weight to work with.
- Use a drill base to ensure your holes are straight. Use a wood boring bit.
- Watch out for the location of the lower mounting holes and your deck. My lower holes interfere with the deck and required some deck work to get access. (my deck was raised 3/4" over stock and is 1" or so thick.)
- Mounting height of the jack plate was an educated guess.
- Buy the Bob's thru-transom fittings and use 4 hoses. Otherwise you have to drill big holes in the transom to get the hose and fittings to pass ( I learned about the thru-fittings too late).

Here are a couple of pictures. The filled holes are from my first idea to use a simple 30", single engine bracket.

https://www.amazon.com/photos/shared/CY ... M0gLR7rT31

Found a shot of the inside. https://www.amazon.com/photos/shared/co ... G_aep2NXnR

The holes with the red plugs are for the jackplate.

this last post is going to help me quite a bit, the nida core I laminated for the deck is 1" thick and it will sit on top of where the original deck would have sat. I'm probably going to have to deal with the same problems you have as well.

I'm becoming more and more convinced that I need to buy the bracket and test mount it and figure out where everything is going to land so I can make accommodations in advance.