Re Propping 83 Merc on 72 Seafari

[Fr. Frank]

Denny's pretty close. Something on the order of a 13x15 cupped SS should be close. SS is much better for offshore. Don't use the Quicksilver Laser II, though, as it's designed as a bow-lifting prop and you need more sternlift. The Vengeance series is okay, but just okay. The old SS Black Max props (no longer made in SS) are better, or best, IMO, the PowerTech M135 series in a 15P.

Denny's right about the mounting position, too. Bottom of the engine cavitation plate about 1" above the keel line with the motor at neutral trim (parallel cavitation plate and keel line)

As an "old hand", I'm gonna throw some useful info at you, but it'll be a bit wordy.

The inline 6 "Tower of Power" Mercury motors are fantastic motors and nearly bulletproof when cared for, but there are some idiosyncrasies to worry about. Never, Never run these motors between 6200 and 6900 rpms - they'll self-destruct quickly from engine harmonics. (Believe it or not, running higher rpms than that is okay up to about 9000 rpms, as long as you run the right fuel-oil mix. Mercury Marine used to race these motors turning 8000 to 9000 rpms, making over 225 hp out of the 115/125 hp motors, and over 250 out of the inline 150 motors.) But these motors love to run at 5400 to 6000 rpms. I have owned no less than 9 inline 6 Mercury motors in my life, and still have an '86 115 in the shed.

I suggest you be very careful with the fuel/oil mixture, based upon your average rpms. If you run mostly over 4800, I suggest a 40:1 mix rather than 50:1 mix, that'll keep your top cylinder better lubed. However, if you run mostly below 4800, stay with the 50:1, or your spark plugs will need periodic cleaning.

Very important - make sure you have a good thermostat. With water temps below 70* and no thermostat, you'll burn fuel very inefficiently, and foul your spark plugs quickly because the motor won't ever get up to a good operating temperature. You can run without a thermostat in water above 80* in Florida in the summer if you have a brand-new impeller, but it's not a good idea, generally.

Speaking of that, make sure you change your water pump impeller every year, or every 100 hours, whichever comes first. This is another Very Important Procedure. Even if you only put 20 hours on the motor one year, change the impeller anyway. More inline 6 motors are killed from overheating than any other cause, and old pumps sometimes fail to adequately cool the top cylinder, especially if the thermostat is stuck open or missing.

Every time you run it in salt, rinse and flush thoroughly. Use Boeshield or Fluid Film on the motor liberally.
Run PowerTune through all three carbs while running in gear a couple of times a year, or run RingFree a couple of times a year.

It's a very good motor. It's also the genesis for the current Verados, because it's a naturally balanced motor.

Don't expect great fuel economy, but they're still better than the OMC motors of the '70 to '87 time frame, just nothing like today. Your cruising rpms for best economy with this motor will likely be near 4800 rpms.

[McGillicuddy]

Hi guys,
Thanks for the pics and advice from the THT site, Big. Is that Bruce Brown video available - does it have a name?
I got the brochures, bushwacker, Muchas gracias!
Thanks for the words of wisdom, Fr. Frank. The more the merrier. Any thoughts on this transom - It looks like its center got cut down to allow for a shorter shaft. I think the current motor is a 20".
Someone tried to seal the cut with Formica and the glue has released so the wood is exposed. I was thinking I'd start by soaking it with some CBES then covering and shaping with mat and resin or Smiths building epoxy. I suspect I'll need to remove the motor to do this right and so I wonder if I should remove the aluminum plates too to make sure there's nothing wrong there. Any thoughts on this? Products, approaches? I'm a decent woodworker but not very experienced with marine f-glas, fillers or gel coat finishing techniques. Thanks again, guys.

[Fr. Frank]

Your transom looks like someone already replaced the wood in it, but had no idea how to seal it, which makes me wonder how good of a job someone did. The plates are an obvious attempt to strengthen a weak transom, and the Formica is a disaster waiting to afflict you. Yeah, you gotta pull the motor off to fix it. Your transom is scary.

If necessary, replacing the transom can be accomplished structurally in as little as 3 days, if you plan ahead. Cosmetics stuff I don't know about.

There's lots of information on that subject here at Classic SeaCraft if you search for it.

[McGillicuddy]

Hi Fr. Frank, and all,
Thanks for the feedback. Bushwacker made some suggestions on products and approaches in an e-mail so thanks to you too, bushwacker. I kind of wondered about that transom fiddlin', because the material appears to be Fir or Cypress and shows a lap-joint. I was under the impression that the transoms on these things were lots of f-glass and resin over 1-3/8" ply., also the transom has been painted with something other than marine quality paint or gel coat as its faded and flaky. The transom is strong however -- and my mechanic and I both rocked on the motor pretty hard with no movement to the transom. I kind of think whoever cut down the transom & bolted on the aluminum plates did so knowing they needed to counter the loss of rigidity from messing with the original transom. Don't know why I give these guys the benefit of the doubt...? After all a lot of guys around here claim to be auto-body workers but they would have had a tough time passing a fifth grade pottery class...,heh, heh

By the way today I went down to work and I immediately noticed an old red Seafari 25 w/NY tags at my shipping terminal, apparently on its way to the Island State... Hope I haven't violated anyone's privacy but just in case I'll leave her name out of this...Never seen a 25 before. That's a lot of boat!!! -- G

[oldbluesplayer]

another Seafari 20 owner chiming in - you will love that boat, and, contrary to what some will say, a 115 is decent power for her, she should top out around 30 - 33, more than you can run is open sea anyways. I wouldn't go beyond that motor-weight range, or the old Johnson V-4, without raising the transom to 25".

Fr. Frank is the man when it comes to the old Merc's, listen to him.

And as others have said, that transom work looks a little scary. If you say it's solid, for now, ok, but from the looks of it, I think you want to plan a transom rebuild, combined with raising to 25", within a few years, coinciding with the future repower.

Fun, and very capable, boat.

Bill

[McGillicuddy]

Thanks Oldbluesplayer Bill, I appreciate the advice. I'm going to try to run this merc while I try to save for a repower. The transom I will try to at least inspect and correct before the Spring fishing season picks up but I'll have to wait to raise the transom due to this 20" shaft. BigShrimpin sent some pics of his and the idea of a full transom w/bracket is very appealing, although the expense or project might be out of reach at least for now. The first thing I need to do is change the bunks on this over-sized trailer (one of them had a bolt digging into the hull). Next up transom seal and rewire. Looking at Blue Sea Systems battery switch w/ charge relay system to isolate starer and house batteries.

Any thoughts pics or ideas are welcome. --Gill

[Bigshrimpin]

The Bruce Brown film was done for Seacraft back in 73 or 74 the title is called "a long way in a small boat". Trayder is the man to talk too about this movie, but I have some info that BBF might be helping Potter get the film restored. It's an amazing short film with awesome footage of 2 23's in some really nasty seas . . . it puts that tracker seacraft video to shame.