Damn that motor is pretty! I guess you have to wear a starched white buttondown to work on it!!

Ill bet it does 52 MPH (light) when you get it dialed in...

Danny here's how I did mine. I took a 5' piece of aluminum square tubing and jacked it up against the keel of the boat, along that flat spot. Then I tilted the engine so the cavitation plate was parallel to the tubing. I then clamped a piece of 3/4" square wood to the bottom of the plate to get my measurement, In this case it was 3/8"....not good!

After I installed the jack plate I did the same measurement process. And then screwed the jack plate up to where the cavitation plate is 2" above the keel.

Please notice how ugly my engine's lower unit is compared to yours. That's 12 years of being run hard and too poor to buy another one.

If the mod was doing his job he would move this thread from the photo section to the performance section......soon. :)

Sandy- the picture above is exactly what you are looking for....

I spoke to Mike R. From Intl Marine tonight. Top notch outfit-he is willing to trade props and adjust height anytime.

Ken-He said the linkage would not be the problem.

Don-done thanks

Thanks for compliments...my goal is to use it and put wear and tear on it and not hold back and just have fun.

Hey Danny,

Your pics of the AV plate under way look about like mine! Hard to see a white plate under all that white spray! Need to put some black electrical tape on top of it to see it until you get it high enough! I've also attached a pic of the height measurement setup.

Been thinking about comments from Ken and others, and I believe it's hard to conclude anything about prop selection and potential motor issues till you get that AV plate up out of solid water. The propeller hp vs. rpm curves I've seen in Dave Gerr's propeller book look fairly linear, so I would think that you should be able to spin the same prop as a 250 Zuke 10% faster if your motor is really putting out 20% more hp!

Sounds like Don has the motor height dialed in pretty well, although the setback of his jack plate should allow him to run a bit higher than if it was mounted on transom. With 30" of setback, I'm slightly over 4" and it's STILL not high enough! Denny

That's a great deal and I would certainly take him up on that but I'm not sure you will get the height you need without a bracket. The benefit of being able to adjust up without a bunch of effort has been a big plus for me when propping. Some props I tried could handle being higher than others but in the end you need one that will let you spin up to at least 6000 rpm and that is on the low side. Balancing that with the proper motor height will be the magic ticket.

I spoke to Ken at Prop Gods. He recommended the 17p. My anti cav plate looks good in the photo I posted. I believe that I need to raise the motor 1 inch or at get a jack plate and be close 2 inches up and try to keep using the 18.5.

Height first plz.
I`m putting the ole sst 1 on for multiple grounding encounters.

I think you're still a little low, based upon your running photos. You've got serious spray ABOVE the spray deflector, so your cavitation plate which is below that will certainly have water pressure above it. That water pressure above the plate pulls the motor downward, creating significantly more hull drag. It's like having the opposite of a stern-lifting prop.

The advice you're getting here is good: raise the motor first. Then worry about a jack plate, if necessary, and only then try to fly the right prop.

You don't have prop issues. You have height issues. Bring that badd ass bitch over to my yacht club next weekend. We'll use the 4000# sailboat lift and Jack your motor up 2 holes.
That should give you 200-300 rpms.

When I first installed my twin 115's they were too low. 5600 rpms. 2 bolt holes up got them to 5950.

Also, are you trimming that motor until she blowed out??? We're you running WOT into a 3 knot tide??? Wind????

Jenna`s gonna smack yo azz.

Haha. Just kidding!!!!

2 bolt holes will do the trick. Adding some tabs and getting rid of the wedges
will help also. Changing motor height can be done in 1/2 hour or less with proper
tools and a tube of 4200.

My only real question is we don't know Danny's true hull weight. 50 mph should
be doable.

Picked up 200 rpms and 3 mph today- got her up to 47 mph. Less weight, maybe loosened up, and better fuel cycling through the tank. Motor will get raised soon....

Saturday on the Manatee River....

What prop are you using now and what is you WOT rpm? Looks like your right at 41 knots.

I got lot's of different numbers based on tide direction and wind. It's so hard to find a clean place to run without variables that affect what your trying to find a baseline for. The lowest fuel burn at an average cruising speed is going to be the best indicator for propping. Top speed is a dragon everyone seems to chase but in reality the best mpg with an average loading is what needs to be nailed down.

DF300 Update
 

Finally ran the boat after the 20hr service and raised the motor all the way on the transom. Hit 6K RPM's for the 1st time with the 18.5 prop. I was at 48 mph at 6K with 3 people and 1/2 a tank. My slippage is only 6% according to Mercury's calculator. Looks like I'm dialed as much I am going to get dialed! Put about 65 miles on her yesterday.

Jonas had a good time handling her for half the trip. Personal auto pilot!

That sounds great Danny.
She will loosen up with more hours.
6% is a strong number.

Thanks Sandy. I am so pleased with it! I have to say, being jacked that high with low slippage, those new lower units do NOT need to run low like the 1st gen lowers. I know offshore you run slower, but running close to 50 to get out to Tampa Bay and back to the ramp sure feels good.

That is what makes us smile.

That and replacing tanks and hoses...

Outstanding Danny, the best part is getting those 65 miles at half the $$$ it would cost me with my old EFI clunker!!! :)

Don-It's crazy, the efficiency is 4mpg at 25mph!

I hope that made you feel better!!!! :) I only dream about 2 mpg and that's going down hill, with the tide and with a tail wind!!

lol, that good feeling is offset by the price tag(as you know, the gas savings will never offset unless I go to the Bahamas 2-3 times a year! Not a bad way to get my money's worth!), but your motor is reliable and you can do what ever you want with that cash difference!