Posted by MarkCz on 09/27/16 - 5:56 AM
#1
I am a new member here. I just purchased a pristine 1987 Montauk that has a 1987 2 stroke Mercury 70 hp outboard. While the motor and engine are in very good condition the propeller is a little beat up. The engine presently is mounted with a cavitation plate even with the hull bottom. I have read that I should move it up 2 holes so the cavitation plate is about an inch to 1.5 inches higher than the hull bottom. I will be running this boat in some choppy water and may need to maintain plane at lower speeds. I am also looking to get decent fuel economy. Top speed is not too important. Can anyone recommend a prop for this combination? I look forward to start contributing to this forum.
Posted by mtown on 09/27/16 - 4:05 PM
#2
Welcome. I agree that you should raise the motor 2 hole up. As to the prop, I have searched and not found the prop info on the SS prop I gave my son in law for his Montauk. His motor was a 90 hp Merc of about the same age as yours.
All I can offer is the following. My 16'7" [not Montauk] has a 17K prop which is Yamaha painted ss the motor is 90 hp 2- stroke Yamaha.
I would definitely buy stainless. At least where I live there are many used for sale at very good prices. Once you are confident what you need that is a good way to go.
Prop experts will chime in hopefully.
Posted by Finnegan on 09/28/16 - 2:07 PM
#3
Your engine has a 2.33 gear ratio, and according to Mercury propeller charts and information, you would need a 17" pitch for heavy load carrying, or a 19" pitch for lighter loads. Your top speed will be around 36-40 MPH. The engine redlines at 5250 RPM.
If you are in the aluminum price range, the best you can buy is a Mercury 4 blade Spitfire (also sold as a Quicksilver Nemesis). These are the best performing aluminum props made, and give good acceleration and low speed planing. I would try 19" pitch.
If you want top of the line SS, Mercury has recently brought out a variation of this prop, called a Spitfire X7. Cost is about $390 delivered. Mercury is claiming this is the fastest and best performing propeller available for any 70-125HP engine, period. I have not yet tried one.
The mid range Mercs have a "taller" mid-section height than most engines, so I would mount the engine in the third (middle of five) hole.
That is all the height you can use or need for a low HP engine like a 70.
You can research the Spitfire props at mercurymarine.com, and find good pricing for them on-line. Also search for the Nemesis, which is identical but sold on the after market.
Posted by MarkCz on 04/15/17 - 6:57 PM
#4
Just reporting back on the new Quicksilver Nemesis 13 X 17 prop on my 1987 Whaler with a 1987 70 hp Mercury 2 stroke. I love this propeller and it suits my needs for a prop that can get the boat up on plane at low speeds since I do most of my boating in areas with a slight chop and I like to be able to get up on plane at lower speeds. We were able to get my Montauk up up on plane with a person load of 600 pounds and 15 gallons of fuel at only 10 mph. Top speed at WOT (5100 rpm) was 31 mph in a slight chop. Thanks for the suggestion I can't ask for a better prop for the money.
Posted by MarkCz on 04/15/17 - 7:14 PM
#5
I thought I would add some info on how I raised the engine on the transom. I bought a Mercury lift ring off amazon that screws into the crankshaft in the middle of the flywheel. I set up a little giant ladder (A frame steup) over the motor and attached my 1,000 pound rated ratchet strap I use to hold the boat on the trailer to the top of the ladder and the other end to the lift ring. After tightening the strap so it was holding the weight of the engine I removed the bolts and then used the ratchet strap to raise it up two holes. My son pulled the motor a few inches away from the transom while I removed the old sealant and we then reinstalled the bolts with new sealant. Painless and took just an hour. This same setup to hold the engine weight would be useful for changing the tilt tube on an engine as well.