What to expect from 20 HP?

[freeisforme]

I picked up a nice clean older Mercury 200 today, it's a good match for my 14' aluminum boat.
The motor runs like a top, has seen only freshwater use, has a reman power head last season, done a local dealer, new water pump kit and a resealed lower unit. All still under warranty. I test ran the motor on the sellers boat, it outrigh flew on a 16' flat bottom boat but I had no real means of figuring top speed and really didn't feel I got it anywhere near its top speed with that motor.

My question is, what should I expect from a healthy Mercury 20 HP 2 stroke on a 400 lb 14 1/2' flat bottom V hull with two guys and gear in it totally around 600lbs. (Boat has a 1150lb max and a 25 hp max). I was going to buy a newer motor but this came about, and at a price I couldn't refuse.

I have the chance to sell it for a decent profit but if it will do the job on my boat, I don't see the sense in selling it since I own it really right.

$120 sure beats $3200 or for a new motor which I was looking at, and the older motor is a good bit lighter than the new 4 stroke.

I would be more than happy if this tops out in the 25 to 30 range, I had a similar boat with a 15 hp that ran out at about 23, so this should be a bit stronger than that boat, plus this boat is a lot lighter than my old boat, by at least 300lbs or more.

Of course this is assuming that this motor is propped to match the boat for recommended RPM.
Anyone have any examples out there running one of these older Mercs on an aluminum boat?

 

[tashasdaddy]

Re: What to expect from 20 HP?

it will plane out nicely, speed depends on load balance in the boat, proper prop, and engine height.

 

[ezmobee]

Re: What to expect from 20 HP?

I think your boat is going to haul ***** with that motor. My uncle has a fairly heavy 14' tinny with a 9.9 and it moves quite well. So I'm sure your 20 will be great!

 

[bigskiohio]

Re: What to expect from 20 HP?

I use to have a 14ft starcraft with 15hp , that was lowest i would go, a 20 should be about right but why not try it then make up your mind .Your fast may not be my fast.

 

[jbjennings]

Re: What to expect from 20 HP?

The 70's merc 20hp motors were beasts on torque and speed. If you put a 2 blade prop on it and just you in the boat, you will likely outrun a 25hp johnson with no problem. However, that motor pushing 600lbs of equipment will be in a bind and will need the right prop. Those motors will rev high with a light load and 2-blade prop and make a really cool rrrrr---rrrrrr--rrrrrr noise in the powerhead that's incredibly distinctive of 20horse mercs. I love them, but...............

If it's pre-1976 it has a mild steel driveshaft that is prone to pitting and wearing out drive shaft seals immediately. A speedi-sleeve will likely solve that problem but I've never used one. I'm very suprised the powerhead on yours needed rebuilding because the lower units usually go long before the powerheads on those. Actually, without an overheat those merc 200 powerheads are nearly indestructible. You'll see tons of those motors that still run great but have no lower unit on them. They also can be bears to start if not tuned perfectly when it's cold outside. The bearing carrier is also hard as heck to get out without the mercury tool. And lastly, the electrical parts (and it has a bunch of em, i.e. trigger, powerpack, etc.) on that motor are really high in my opinion.

Basically, I'd check that lower unit for water and unless it was water free, I'd sell it. If the wires under the cowl looked corroded or were stiff, I'd sell it. If it runs perfect and has a well-sealed lower unit, it's an AWESOME motor. They were real jewels when new.
JBJ​

 

[OldMercsRule]

Re: What to expect from 20 HP?

I have a 1986 14' high gunnel heavy gauge aluminum SeaNymph, (purchased new), n' I never weighed it so dunno what it actually weighs.

It is rated fer a 25 HP engine.

I have had my 6 HP crank rated Johnny on it which plans it with one or two people in it, three people: NO PLANE.

I ran it with a 1974 crank rated 25 HP Johnny, (the small high reving 25 HP Johnny of that era), and it went 28 MPH with one person and was a great power combination fer that skiff. Johnny eventually got tired from many hours of use so I now have me prop rated 1996 25 HP Merc on it, (prolly 20 lbs heavier engine then the old Johnny was), and it does 33 MPH with one person. I over load that skiff many times, (if the lake is flat calm), fer the 5/8 mile trek from me dock on shore to RR island and it was impossible to stop either the Merc or the old Johnny from gettin' on step with a very heavy load.

Very good combination!!! Luv the boat.

Yer 20 HP Merc would likely be faster or at least as fast as the old Johnny, not quite as fast as the 25 Merc, dunno how heavy yerboat is but it should be a very good combination.

Good luck. JR

 

[freeisforme]

Re: What to expect from 20 HP?

The 70's merc 20hp motors were beasts on torque and speed. If you put a 2 blade prop on it and just you in the boat, you will likely outrun a 25hp johnson with no problem. However, that motor pushing 600lbs of equipment will be in a bind and will need the right prop. Those motors will rev high with a light load and 2-blade prop and make a really cool rrrrr---rrrrrr--rrrrrr noise in the powerhead that's incredibly distinctive of 20horse mercs. I love them, but...............

If it's pre-1976 it has a mild steel driveshaft that is prone to pitting and wearing out drive shaft seals immediately. A speedi-sleeve will likely solve that problem but I've never used one. I'm very suprised the powerhead on yours needed rebuilding because the lower units usually go long before the powerheads on those. Actually, without an overheat those merc 200 powerheads are nearly indestructible. You'll see tons of those motors that still run great but have no lower unit on them. They also can be bears to start if not tuned perfectly when it's cold outside. The bearing carrier is also hard as heck to get out without the mercury tool. And lastly, the electrical parts (and it has a bunch of em, i.e. trigger, powerpack, etc.) on that motor are really high in my opinion.

Basically, I'd check that lower unit for water and unless it was water free, I'd sell it. If the wires under the cowl looked corroded or were stiff, I'd sell it. If it runs perfect and has a well-sealed lower unit, it's an AWESOME motor. They were real jewels when new.
JBJ​

Its got a 2 blade prop on it now and came with two other spares, as well as two other lower units. The lower on it now is supposedly all rebuilt and resealed, the parts list shows a new driveshaft, and new prop shaft, but that was three years ago.
The wiring is all new, brand new harness and plug, all the bolts in the power head are brand new stainless steel, I can see that all the gaskets have been changed, the carbs are clean and freshly done, and its got electric start. It cranks about three times with the choke on cold, sputters, then fires and runs fine once I push the choke in one click. It was 39 degrees out this morning when I tried it. The lower unit fluid has no water in it, but I changed it anyway, there's no sign of metal or debris either.
I was actually leary of the 2 blade prop for power, but I guess I'll give it a try. (I have a 3 blade from an another motor I used to have).

It sounds great when it runs, it got the sellers boat on plane with me and him in it nearly instantly but that was a flat bottom bass boat with no weight other than the two of us and a fuel tank. He didn't even carry a battery for the starter, he just rope started it. It has a 5 pin side plug and a remote ignition switch, but the rest of the controls are on the motor.

Its actually hard to shut down, someone put a kill switch on the motor, (replaced what ever it had originally with a heavy toggle switch, and if you don't let the motor come to an absolutely complete stop, it will restart as soon as you let off the switch.

It came from freshwater and it looks like it, even where there is paint loss, the metal is still clean. Absolutely no corrosion on this at all. Even the original steel fuel tank is rust free, something that you just don't see in this area.
I do want to put the right kill switch back on it, it just don't look right with a toggle switch, and I'd love to find an on the motor starter button too. I'm not sure what they would have used?

 

[jbjennings]

Re: What to expect from 20 HP?

I'd buy that motor. It sounds like someone really put some time and money in it, and almost surely put a stainless shaft in I would think.
I went to the local farmer's hardware store and got a sealed rubber switch that they use on tractors and it fit great on my merc 9.8 and looked similar but better than the factory switch for about 15 bucks. The extra props are awesome. You can have the high speed 2-blade when you go by yourself, and the 3blade for buddies. It has more than enough power for 2 guys.
Good luck and neat find. I'd love to drool over a pic if you get a chance to post one. The e-start is a SUPER feature on that merc.
Here's a pic of my 9.8 merc and other favorites:
JBJ​

 

[freeisforme]

Re: What to expect from 20 HP?

No pics yet, but I'll get some hopefully this weekend.

I think I did alright with this motor for $120. It runs like a top and it did nothing wrong on the test run we took in his boat with it. I was actually expecting it to run a bit slower than it did in his boat, it was up on plane pretty quick for being just a 2 blade prop and only a 20 hp on a boat rated for 55 hp. Mine is a lot lighter and probably a lot sleeker in the water.
His boat was one of those 16' big jons with an all welded hull and flat bottom.
Although it was empty except for him, me and the fuel tank, it still is probably heavier than my boat. I have a wood floor, and wood seat bench tops, and will carry a pair of batteries and most likely a pair of tanks, I think my boat still probably takes less to move through the water. I ran it when I first got it with an 8 hp Suzuki 4 stroke that came with it, it did 18 mph with just me and the fuel tank onboard in choppy water. I sold that motor, and was planning on using my 9.5 Evinrude, which moves it at about 20-22mph with just me and a light passenger and only a 3 gallon tank. It does better on slightly choppy water.

I also have a manual only Evinrude 25 hp, that runs great but it's a long shaft and I've had no luck finding a short shaft lower unit. I did hang it for a test run, even though it's too long, it did get up to 26 mph on the gps, but it that was with just me and a tiller extention.
I'd be more than happy with 30 mph, even 28 I guess.
I like staying with the 2 stroke for the weight factor, I was afraid to hang the heavier 4 stroke motor on it. The 20 hp is heavy enough in my opinion.
The fact that this motor also has electric start is a big plus, as well as the fact that it will also charge the battery.

As soon as the weather warms up a bit again, I'll be replacing the transom wood, it's not really rotted but it's original, and easy to change. I think with the larger motor it will need all the strength I can give it.

Also, should I use an external transom board to protect the hull on this? I see most boats with something there, this boat never had a real motor, and even the trolling motor leaves marks in the outer hull skin. I'm thinking of making a 3/8" plywood plate to go right under the motor bracket on the outside?

 

[jbjennings]

Re: What to expect from 20 HP?

You'd better make sure that transom is in good shape because a 20hp merc will do a lot of wrenching on the transom corners. I'd be in the poorhouse if I could find too many of those for $120! You might have gotten the best deal you'll ever get on an outboard. A small piece of plywood wouldn't hurt at all on the outside of the transom. If a wimpy 9.5hp OMC ran your boat 20 to 22, then you'd better be careful with that 20! I wouldn't doubt if it ran your boat with just you in it close to or slightly above 30mph with the 2-blade prop.
I'm really jealous of your find! Is it a blue band or a red band?
Later,
JBJ

 

[EN2]

Re: What to expect from 20 HP?

When I was about 11 or 12 my dads cousin had one of these on a 16ft Lone star. The thing just flew! Good starter. Had the black rubber cover over the kill switch that had a split in it And would shock you when pushed on it to kill it . Also throttle is bassackwards on this model. Pushbutton shift fwd/rev.

 

[freddyray21]

Re: What to expect from 20 HP?

JB it depends on the year for the ignition. If it's an older one then it still has points and condensers so cheap to fix. If it is an electronic ignition and that quits the the cost to fix it is more than the motor.

 

[freeisforme]

Re: What to expect from 20 HP?

Its a red band motor, a 1970 model by the one website I checked, (Model 2892684), I was assuming that Thunderbolt Ignition meant electronic igition? ("Thunderbolt Ignition" logo on front emblem). The prop on it is pretty large looking but I've not check it's diameter or pitch yet, if it's marked.
The little 9.5 HP Evinrude does real good on this boat, it actually surprised me, but a lot of it's performance is because I can run that with a smaller tank, no battery on board and it's got a 30" extension handle on the tiller and a remote shift cable on that lever. I may adapt that to the Merc instead so I can sit midship. It will do wonders for weight distribution. With the electric start Merc, also comes a larger tank, a battery, and the added weight of the motor itself. It came with a group 27 deep cycle, a battery box, and a remote igition switch and lanyard panel which he had mounted hanging off one rear corner bracket on his boat. I'd like to eliminate all of that and put it all on the motor, leaving nothing but the two battery cables coming into the boat. Right now I have two battery cables, two smaller guage wires to the ignition switch and one pin is unused but has the lead in the external harness. My guess is that it's for a remote choke which it don't have. It only has the manual choke on the panel. Which works fine for me. I'd be just as happy with everything on the motor and a simple pushbutton for the starter. The simpler the better.
I plan to do a double 3/4" ACX plywood transom laminated with epoxy and fiberglass in the middle for added rigidity. I will also ad the outer panel to protect the transom on the outside. I am debating on whether to bolt the motor on or to just use the clamps? The last owner only had it clamped and it seemed to work just fine. (His transom was all aluminum, no wood, and it was a bit battered from the motor twisting into and indenting it just below the motor bracket.

If I were to take an educated guess on the prop size and pitch without measuring it, I'd say it's about a 10" diameter with about a 10.5 to 11 pitch or so. It's a two blade aluminum prop.

 

[freddyray21]

Re: What to expect from 20 HP?

that is one of the expensive ignition. 275.00 for the stator if it quits. run it and see. may not have a problem for years or never.

 

[Mark_VTfisherman]

Re: What to expect from 20 HP?

...I am debating on whether to bolt the motor on or to just use the clamps?...

Use the clamps AND bolt it. Bolts are much better to use in a downturn economy if you know what I mean. Make it difficult and stuff sticks around better. Locks don't always work but making it not worth it does.

 

[freeisforme]

Re: What to expect from 20 HP?

The only problem with bolting it on is that I'll have two holes to plug when running a smaller motor in lake here, (10HP max). I still plan to swap back and forth between the 20 and the 9.5 Evinrude and maybe even a 15 HP Johnson if I can find the parts to convert it to a short shaft. The original plan was to rig this with a jack plate and run the long shaft motors and posibly by a new Yamaha 20 four stroke for it, also in a long shaft. But since I found this Merc 20, I'll keep running he 9.5 on this one and just keep the long shaft motors around for what ever comes down the pike next.
(I have two 9.9 motors and a 15hp, all in the mid 80's with very low hours, but all are long shaft motors).
I like the idea of having electric start, but it's not mandatory, if I can convert the 15 to a short shaft, then I'd just label that as a 9.9 and have electric start on both motors.

This boat moves pretty easy, it does really good with just the 9.5 HP so it's bound to fly with the 20hp Merc. I don't worry much about the stator on these, I test ran this motor before buying it on the sellers boat for about 5 miles or so, running it like a stole it to boot. It was downright fast on his flat bottom, which was larger than my boat, definitely wider by a foot or so, and me and him, plus fuel and a battery had to be over 700lbs.

I think what's most important to me is getting on plane, and staying there. It does just fine with the 9.5, so I don't have any doubts about the 20 doing the job, it's got to be faster. I used to have a 15' modified V jon boat with a full interior, decks, and livewell, and two pedestal seats on which I had a 15hp Mariner, it ran about 22 mph with two big guys, two 6 gallon tanks of fuel, and twin Group 27 batteries. It had a side console and steering too. That boat was heavy, it was too heavy to lift, I couldn't lift either end off the trailer, even when it was new. This boat I have now is light, really light compared to that boat. I can lift this boat with no real effort.

My biggest concern is will it make up for it's own added weight over say a 15HP evinrude e start, tiller steer, which is far lighter.

 

[OldMercsRule]

Re: What to expect from 20 HP?

I would not drill holes in the transom on a small boat that you use muliple engines on. Buy a locking device that locks the engine on the transom over the transom thum screws.

JR

 

[hipster dufus]

Re: What to expect from 20 HP?

my 1444 g3 with a 9.8 tohatsu, tops out at 19.1 mph. that is with just me and one of my batterries.with 2 guys and 2 batts,11 mph.with 2 guys and 1 batt, about 14 mph. i played with the trim some to get these numbers. it is a 4 stroke engine. i can tool along all day at 12.it works fine for me.

 

[Wee Hooker]

Re: What to expect from 20 HP?

FWIW, I was running a 15 hp on a similar size & weight boat. I was gettign 17-19mph with two guys and gear. 23-25mph solo. As mentioned it's hard to compare though. Too many variables. That motor (IMHO) should be sweet on your boat.

I like to bolt and clamp. I've seen 2 clamped motors come off in an impact. It also makes it harder to walk off with. That said,
I also use the lock that covers the clamp. A new 20 hp is over two grand. The lock is $25 and worth the piece of mind.

 

[freeisforme]

Re: What to expect from 20 HP?

I don't have to worry much about motor theft, I pull the motor when I park the boat and keep the motor on a stand in the garage.
The garage is alarmed and within firing range.

I too have seen motors come in the boat after an impact, but a safety chain can help stop that. The hassle of dealing with bolt holes when running my 9.5 HP motor isn't worth all the agravation in having to make sure they're plugged up when not in use. What I will do is add an exterior motor plate to pad the transom, I'll most likely just glue it in place with some 5200, or secure only the top edge.

I will be redoing the transom, fresh wood is a must.

I ran a 14' Starcraft thats a bit lighter than my boat but similar in layout today with an older West Bend 20 HP on it, I took my GPS, and with me and another passenger, plus a 3 gallon tank and trolling motor and battery, it got up to 26.5 mph on the river, and the motor didn't seem to be hitting full RPM, so it may have been propped wrong or for less weight.
I think my Merc should do a bit better even with more weight. That Chrysler didn't feel all that strong to me.