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I have a 1979 Newport commercial hull with a 1979 Mercury 80 HP with optional PTT, all is in very good working order. I have read the endless benifits of having the motor at the correct height and want to explore doing this on my boat.

This boat was shipped from Boston whaler with no trailer or motor and was set up in 1979 by a dealer in Ontario Canada, the motor, boat and trailer are all original except for upholstery, I am trying to keep it that way

My challenge is that this motor has 4 bolts and 2 clamps, the existing 4 bolts go through into splashwell, no blind holes, how can i raise this type of setup, do i need to get a jack plate, if yes has anyone done this with this type of motor, how do you get the clamps to fit on a jack plate.

Second part of the question is if Ido install a jack plate and eventualy repower do I keep the jack plate?

Last part, if I install a jack plate it will have a certain setback, am I also looking at replacing my steering cable as it might be too short.

This summer I changed from an old Merc 3 blade 19 pitch prop to a new Merc 4 blade 17 pitch prop, significant improvement in hole shot and better prop hold in high speed cornering, great for pulling the tube around as well.

On a somewhat light load, top engine RPM is 5300 and with a top speed of 33 MPH (GPS) i do get a lot of porpoising when trimming out.

At the end of the day I am looking for some improved performance without having to repower, just prepped for winter, gearcase lubricant looked like new when drained and compression is around 125 on all 4 cylinders, no clue on how many hours.

Thanks
Marc

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With four bolts mounting your engine the clamps serve no purpose. I have an engine with clamps mounted with four bolts and if I ever remove the engine I will remove the clamps.

I don't know anything about the PT&T on your engine. On mine I have three or four bolt holes in the PT&T and a slot on both sides. To raise my motor I removed the bolts through the bolt holes and loosened the bolts in the slots just enough to allow the motor to move up or down. Before doing this I placed a piece of wood beneath the engine skeg and raised the front of the trailer enough to cause the skeg to contact the wood. I then very slowly continued to raise the front of the trailer forcing the engine to move upward PT&T to move upward on the transom. When the desired bolt hole was aligned with the desired upper bolt hole in the transom I reinstalled the bolts on both sides being careful to use liberal amounts of Boat Life Life Caulk in the bolt holes. I then removed the lower bolts from the slots and reinstalled them with more fresh caulk.

Bob's your Uncle.

The best height for your engine can only be positively determined by experimentation. I would wait until the next time you use your boat and look at the anticavitation plate while on plane. The plate should be visible with very little water running over it's top surface. What you see should provide a guide of a good starting point when you adjust your engine height.

Once you've adjusted your engine's height you can determine what your propeller needs may be. With luck you will already have the ideal propeller.

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As a life long Merc owner, I am familiar with your engine mounting detail, and raising an engine that uses the old design transom bracket is not easy to do. The side mount power trim cylinders add additional complication. All mid range Mercs 1983 and earlier, did not use the now standard BIA bolt pattern wich offers five holes of height adjustment range, each 3/4" apart.

The bottom carriage style bolts go into a slot, which may allow some vertical adjustment, depending on where the boat transom is drilled. If the bolt is already at the bottom of the slot, you cannot go up any higher without removing the engine and re-drilling. The other critical dimension is how much height adjustment the smaller, single, 3/8" top holes allow for, and if I remember correctly, it's not much, maybe and inch or so at the most. So you can look at the situation and determine how much height you can gain. The thumb screws need not be used if the top bolts can be used without being too close to the top of the transom, and no wood blocking is needed either.

A jackplate is probably the best, but most costly, way to achieve the height flexibility you are after. I recommend a Sea Star Solutions (formerly Detwiler) black anodized manual 6" setback jackplate, which I think is the best brand on the market, and will hold up the best because of the anodized aluminum construction. About $350. I use one of these on my 1979 Montauk which you can see in the personal website link. These older Mercs require a special adapter plate attachment which can be purchased from CMC, which I believe will not only fit the CMC jackplates, but also the Sea Star. This plate allows for the thumb screw clamps. About $100 I believe. I would do some careful research on how this adaptor works and is fitted to a jackplate.

So you are looking at a $500 expense, plus engine removal and transom hole filling work. It may not be worth the expense. But if you decide to do it, you will now have a transom properly drilled for any 1984 and later modern engine installation, since all jackplates are drilled for the standard BIA bolt patter, both on the transom side and the engine side. I am not sure if the jackplates are drilled for the older Merc bolt pattern - some are, some aren't.

I would think your engine, using a 2.33 gear ratio, could turn a 19" Mercury Laser II prop, which should give great overall performance. Also look into the 4 blade aluminum Spitfire/Nemesis, and the brand new Spitfire X7 SS model, now supposedly the hottest mid-range prop Mercury is offering.