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Author Topic:   1985 13-footer, 1973 Merc 500

rogdeny posted 01-03-2012 06:25 AM ET (US)
[Give your opinion] on putting a [1973 Mercury 500 50-HP that weights] approximately 275-lbs on a [1985 Boston Whaler 13-foot boat which] presently has a Yamaha 40 which is pretty much kaput.
Peter posted 01-03-2012 07:03 AM ET (US)
If it is 275-lbs, it is too heavy.
jimh posted 01-03-2012 08:59 AM ET (US)
The maximum horsepower for a classic 13-footer is 40-HP. An old 1973 Mercury 500 was an engine rated for power at the crankshaft, not propeller shaft, so it might only make 45-HP at the propeller, and that was when new. Now that it is almost 40-years-old, it might only make 40-HP at the propeller. I don't see the horsepower limitation for the hull as being drastically exceeded.
That Mercury 500 is a very nice outboard engine. It has four cylinders of 11-cubic-inch displacement. It is a rather smooth running little four-cyclinder in-line engine. I don't think a 1973 has the electronic ignition or THUNDERBOLT ignition, as Mercury called it.
As for the engine weight, at 275-lbs you are approaching a rather large percentage of the hull weight, which should be about 320-lbs. That is a lot of transom weight on a small boat. If Boston Whaler had specified a maximum transom weight for their classic 13-footer, I am sure you would be exceeding it with an engine that weighs 275-lbs.
rogdeny posted 01-03-2012 09:49 AM ET (US)
Thanks to all for your replies. I suspected as much regarding the weight. It's a shame. My Merc 500 is in very good condition (the boat, too). Few hours on it considering its age and run only in clean, fresh water (northern NH). By the way, it does have the Thunderbolt ignition. I think I will start looking for something new, or newer, in the 25 to 35 hp range. Thanks again.
contender posted 01-03-2012 10:01 AM ET (US)
Back in the early 70's late 60's and friend of mined did exactly what you are doing, He tried to race( It was the Mike Gordon or Orange Bowl Classic 100 in Biscayne Bay Miami) the boat (13 Whaler with a 50 Mercury, we even fiberglass a seat in the center of the hull) The transom ended up splitting down both sides and he never finished the race, The engine is just to heavy for the 13 whaler with out any type of modifications to the transom, and then you are also talking about a very old hull.
leadsled posted 01-03-2012 10:16 AM ET (US)
You are way off on the weight of the Mercury 500 ( 50 hp.). I think an electric start engine is around 200. I ran a 1976 Merc 50 hp on my 13' for many years without a problem. I later replaced it with a Merc 500 manual start short shaft which I think was around 180 pounds or less. In any case it not much more weight than one of those Heavy 4 stroke 25 hp engines. Those Merc 500's would push the 13' Whaler to 38-40 mph.
rogdeny posted 01-03-2012 10:33 AM ET (US)
CONTENDER. Thanks for that bit of information. More support for not using the Merc 500 on a 13' BW.
rogdeny posted 01-03-2012 10:52 AM ET (US)
LEADSLED: Thanks for that. I have the official Merc 500 manual but nowhere does it give the weight of the engine. I forget where I got the 275 lbs from. Does anyone out there know for sure the weight of a 73 Merc 500??
Tohsgib posted 01-03-2012 11:36 AM ET (US)
It is 175lbs or so and is by no means too heavy nor would it put a stress crack on a 1985 hull. The old bulkhead style transoms of the 60's were not so strong and hence why they were reworked in 1971. Problem mainly would be reliability from a 40 year old engine. They also had wiring problems where the coating literally crumbles. Lastly look to make sure it is a 20" shaft, they made them in 15" as well. That 4cyl engine is by far the best classic engine Mercury made but again it is 40 years old. Personally I would also buy a CMC PT130 so you have PTnT with it and won't have to drill new holes in the transom since your Yamaha used BIA pattern. The Merc will perform about the same as your Yamaha....maybe a tad faster. Your Yamaha weighs between 172-185 depending on PTnT. Brochure states 158 but I think that is the manual start 15" shaft model.
BQUICK posted 01-03-2012 05:23 PM ET (US)
I don't think a 1973 has the electronic ignition or THUNDERBOLT ignition, as Mercury called it.
Not true....Merc had it since 1968.
A 50 Merc is not that heavy especially compared to today's 4 strokes.
macfam posted 01-03-2012 08:54 PM ET (US)
Back in the 60's, my next door neighbor Rick had a 13 Whaler with the 50 Merc 4 cylinder. Sweet!
That engine is not too heavy. It was manual start and no T & T.
Very fast!!!!
It was that boat as a teenager that made me thirsty for my own 13 many years later.
jaycon posted 01-04-2012 12:57 PM ET (US)
Anecdotally; A friend ran a 13' whaler with a short shaft Mercury 70 for years with no issues. I would mount that 50 and enjoy it. Umm, that did sound odd didn't it?
outragesteve posted 01-04-2012 01:32 PM ET (US)
The Merc 500 (50 HP) is an awesum engine. Lots of torgue, very smooth running, easy starting. Merc also made that engine in a 40 HP that was replaced by the 402, which was 2 cylinders. This engine was a dog compared to the 4 cylinder 40/50 engines. I friend of mine had a pair of 50's on a 1968 16'7" Whaler and it was a blast! He had a ski bar mounted and the boat would yank out two slalom skiers no problem...little heavy in the stern, but what fun!
crabby posted 01-04-2012 03:17 PM ET (US)
Back in the 1970's a good friend dropped a then brand new 50 hp Merc tiller steer on his 13' BW and kicked my butt with my 40 hp 'Rude on a 16' aluminum rig. We used that boat all over the south shore of Long Island and even several miles out into the Atlantic catching fish. However, the Whaler was somewhat modified in that he had glassed up 8 inch high extensions to the sides that ran to about 4 feet forward of the transom to help keep the water and spray out of the boat while he drove from the rear bench. I'll try to dig out some pics for you all.
rogdeny posted 01-06-2012 01:53 PM ET (US)
Thanks to all for you good comments on the Merc 500/13 BW. Come Spring I will put it on the boat and see how it goes.
One question, though. How do you measure the shaft length - from where to where?
Thanks again.
Tohsgib posted 01-06-2012 02:04 PM ET (US)
Post a pic or e-mail me one...easy to see.
Binkster posted 01-07-2012 04:28 PM ET (US)
Measure from the top of the clamp where the motor sits on the boat to the cavitation plate. A short shaft is about 17", a long shaft 22"
Tohsgib posted 01-08-2012 12:08 AM ET (US)
Or....weld up a harmonic balancer puller and some other stuff and lift the engine onto a scale. Send us the weight and we can tell from that. Then again you can use a lifting strap to remove it much easier. :)
Binkster posted 01-08-2012 03:57 PM ET (US)
Nick
:)

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Author	Topic: 1985 13-footer, 1973 Merc 500
rogdeny	posted 01-03-2012 06:25 AM ET (US) [Give your opinion] on putting a [1973 Mercury 500 50-HP that weights] approximately 275-lbs on a [1985 Boston Whaler 13-foot boat which] presently has a Yamaha 40 which is pretty much kaput.
Peter	posted 01-03-2012 07:03 AM ET (US) If it is 275-lbs, it is too heavy.
jimh	posted 01-03-2012 08:59 AM ET (US) The maximum horsepower for a classic 13-footer is 40-HP. An old 1973 Mercury 500 was an engine rated for power at the crankshaft, not propeller shaft, so it might only make 45-HP at the propeller, and that was when new. Now that it is almost 40-years-old, it might only make 40-HP at the propeller. I don't see the horsepower limitation for the hull as being drastically exceeded. That Mercury 500 is a very nice outboard engine. It has four cylinders of 11-cubic-inch displacement. It is a rather smooth running little four-cyclinder in-line engine. I don't think a 1973 has the electronic ignition or THUNDERBOLT ignition, as Mercury called it. As for the engine weight, at 275-lbs you are approaching a rather large percentage of the hull weight, which should be about 320-lbs. That is a lot of transom weight on a small boat. If Boston Whaler had specified a maximum transom weight for their classic 13-footer, I am sure you would be exceeding it with an engine that weighs 275-lbs.
rogdeny	posted 01-03-2012 09:49 AM ET (US) Thanks to all for your replies. I suspected as much regarding the weight. It's a shame. My Merc 500 is in very good condition (the boat, too). Few hours on it considering its age and run only in clean, fresh water (northern NH). By the way, it does have the Thunderbolt ignition. I think I will start looking for something new, or newer, in the 25 to 35 hp range. Thanks again.
contender	posted 01-03-2012 10:01 AM ET (US) Back in the early 70's late 60's and friend of mined did exactly what you are doing, He tried to race( It was the Mike Gordon or Orange Bowl Classic 100 in Biscayne Bay Miami) the boat (13 Whaler with a 50 Mercury, we even fiberglass a seat in the center of the hull) The transom ended up splitting down both sides and he never finished the race, The engine is just to heavy for the 13 whaler with out any type of modifications to the transom, and then you are also talking about a very old hull.
leadsled	posted 01-03-2012 10:16 AM ET (US) You are way off on the weight of the Mercury 500 ( 50 hp.). I think an electric start engine is around 200. I ran a 1976 Merc 50 hp on my 13' for many years without a problem. I later replaced it with a Merc 500 manual start short shaft which I think was around 180 pounds or less. In any case it not much more weight than one of those Heavy 4 stroke 25 hp engines. Those Merc 500's would push the 13' Whaler to 38-40 mph.
rogdeny	posted 01-03-2012 10:33 AM ET (US) CONTENDER. Thanks for that bit of information. More support for not using the Merc 500 on a 13' BW.
rogdeny	posted 01-03-2012 10:52 AM ET (US) LEADSLED: Thanks for that. I have the official Merc 500 manual but nowhere does it give the weight of the engine. I forget where I got the 275 lbs from. Does anyone out there know for sure the weight of a 73 Merc 500??
Tohsgib	posted 01-03-2012 11:36 AM ET (US) It is 175lbs or so and is by no means too heavy nor would it put a stress crack on a 1985 hull. The old bulkhead style transoms of the 60's were not so strong and hence why they were reworked in 1971. Problem mainly would be reliability from a 40 year old engine. They also had wiring problems where the coating literally crumbles. Lastly look to make sure it is a 20" shaft, they made them in 15" as well. That 4cyl engine is by far the best classic engine Mercury made but again it is 40 years old. Personally I would also buy a CMC PT130 so you have PTnT with it and won't have to drill new holes in the transom since your Yamaha used BIA pattern. The Merc will perform about the same as your Yamaha....maybe a tad faster. Your Yamaha weighs between 172-185 depending on PTnT. Brochure states 158 but I think that is the manual start 15" shaft model.
BQUICK	posted 01-03-2012 05:23 PM ET (US) I don't think a 1973 has the electronic ignition or THUNDERBOLT ignition, as Mercury called it. Not true....Merc had it since 1968. A 50 Merc is not that heavy especially compared to today's 4 strokes.
macfam	posted 01-03-2012 08:54 PM ET (US) Back in the 60's, my next door neighbor Rick had a 13 Whaler with the 50 Merc 4 cylinder. Sweet! That engine is not too heavy. It was manual start and no T & T. Very fast!!!! It was that boat as a teenager that made me thirsty for my own 13 many years later.
jaycon	posted 01-04-2012 12:57 PM ET (US) Anecdotally; A friend ran a 13' whaler with a short shaft Mercury 70 for years with no issues. I would mount that 50 and enjoy it. Umm, that did sound odd didn't it?
outragesteve	posted 01-04-2012 01:32 PM ET (US) The Merc 500 (50 HP) is an awesum engine. Lots of torgue, very smooth running, easy starting. Merc also made that engine in a 40 HP that was replaced by the 402, which was 2 cylinders. This engine was a dog compared to the 4 cylinder 40/50 engines. I friend of mine had a pair of 50's on a 1968 16'7" Whaler and it was a blast! He had a ski bar mounted and the boat would yank out two slalom skiers no problem...little heavy in the stern, but what fun!
crabby	posted 01-04-2012 03:17 PM ET (US) Back in the 1970's a good friend dropped a then brand new 50 hp Merc tiller steer on his 13' BW and kicked my butt with my 40 hp 'Rude on a 16' aluminum rig. We used that boat all over the south shore of Long Island and even several miles out into the Atlantic catching fish. However, the Whaler was somewhat modified in that he had glassed up 8 inch high extensions to the sides that ran to about 4 feet forward of the transom to help keep the water and spray out of the boat while he drove from the rear bench. I'll try to dig out some pics for you all.
rogdeny	posted 01-06-2012 01:53 PM ET (US) Thanks to all for you good comments on the Merc 500/13 BW. Come Spring I will put it on the boat and see how it goes. One question, though. How do you measure the shaft length - from where to where? Thanks again.
Tohsgib	posted 01-06-2012 02:04 PM ET (US) Post a pic or e-mail me one...easy to see.
Binkster	posted 01-07-2012 04:28 PM ET (US) Measure from the top of the clamp where the motor sits on the boat to the cavitation plate. A short shaft is about 17", a long shaft 22"
Tohsgib	posted 01-08-2012 12:08 AM ET (US) Or....weld up a harmonic balancer puller and some other stuff and lift the engine onto a scale. Send us the weight and we can tell from that. Then again you can use a lifting strap to remove it much easier. :)
Binkster	posted 01-08-2012 03:57 PM ET (US) Nick :)