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1978 Montauk lists to port with new 90HP Mercury 4 stroke
Rockfish	#1  Posted on 08/29/20 - 10:08 AM
Member Personal Page Posts: 6 Comments: 0 Joined: 03/27/07	I recently had a 90HP 2019 Mercury 4 stoke put on my 1978 Montauk 17. Prior to that it had a 1995 Johnson 88 SPL and prior to the 88SPL a 1977 Johnson 70HP. Both were mounted all the way down on the hull. It ran fine with both prior motors. With the new Mercury the boat lists to port significantly when on plane over 3000 RPMs and is somewhat "heavy" steering. Top running RPMs are 4900 with 3 adults in the boat. The boat runs straight and does not seem to pull port or starboard. The battery is mounted in the back on port side and counter balanced with the anchor and box on the starboard side in the back. The gas tank (22 gal Moeller) is located under the RPS seat. The Mercury has: 1. Trim tab is under the Anti Ventilation Plate (AVP) and is straight. 2. The prop is 3 blade, 13" diameter, 19 pitch Mercury Black Max 77346A45-19P. 3. The AVP appears to be parallel and even to the bottom of the hull. 4. The motor is mounted all the way down on the hull (first top hole) using the existing BIA holes. 5. The motor has been lagged screwed at the bottom below the drain holes (hole #3 of 5 holes) which I don't particularly like. Trimming the motor up or down does not stop the listing while on plane. Questions: 1. Is the prop size correct? 2. Should the Trim Tab be adjusted? 3. Should the motor be mounted higher at least Two Holes Up (third hole) for starters? I'm taking the boat back to the Mercury dealer to discuss how to remedy and would appreciate comments from our group. Thanks.
Phil T	#2  Posted on 08/29/20 - 11:02 AM
Administrator Personal Page Personal Album Project Albums Posts: 6994 Comments: 6 Joined: 03/26/05	Bill - The port list is due to the engine being mounted too low and trim anode slightly out of alignment. You need to have the engine removed. Fill the "blind" holes with hardwood plugs, dipped in epoxy, trim excess and cover with locktite marine expoy - white which dries to a close match to white/Desert tan. Redrill lower holes per BIA standard. Mount the engine so the anti-cavitation plate is 1-1/2 inches above the bottom of the keel or 2 holes "up" (top bolt is in 3rd hole down from top). Substitute the aluminum prop for 13.15x18 Mercury Vengence. This information comes from Boston Whaler 16'7/17 owners who have installed new Mercury 90 hp FourStroke motors. With 3 people, expect WOT to be ~40mph at 5500 rpm. Running light/solo expect WOT to be 45 mph at 5900 rpm. 1992 Outrage 17 I 2019 E-TEC 90, Viper 17 2+ 2018 Load Rite Elite 18280096VT
Rockfish	#3  Posted on 08/30/20 - 12:19 PM
Member Personal Page Posts: 6 Comments: 0 Joined: 03/27/07	Phil, thanks for your reply.
biggiefl	#4  Posted on 08/31/20 - 7:26 AM
Member Posts: 890 Comments: 4 Joined: 05/08/06	What Phil said 24 Whalers so far....
Rockfish	#5  Posted on 09/03/20 - 5:15 PM
Member Personal Page Posts: 6 Comments: 0 Joined: 03/27/07	Again thanks Phil and biggie. Met with dealer today. He wanted the new BIA hole diagram as posted in article. Agreed to move engine up 1 1/2” (3rd hole - green ones), fill old holes and use 4 through bolts. Also putting on a different prop. He even volunteered to take it to the river and test run to see if trim tab Needs adjusting and if it’s running level. They repower a lot of boats there including whalers. They had a Tow Boat Whaler as well as 3 other Whalers. He said it should run 55-5900 rpm as you said. Let’s hope it solves the problem.
Joe Kriz	#6  Posted on 09/03/20 - 5:53 PM
Site Owner Personal Page Personal Album Photo Albums Project Albums Posts: 11434 Comments: 452 Joined: 03/18/05	Phil T wrote: Bill - Redrill lower holes per BIA standard. You cannot redirill the lower holes to BIA standard in a 1978 Montauk. The splaswell is not deep enough in the early Montauk's. As Rockfish mentions, he needs to drill the lower "Green" holes in our diagram. https://www.whalercentral.com/article...icle_id=82
Rockfish	#7  Posted on 01/04/21 - 4:40 PM
Member Personal Page Posts: 6 Comments: 0 Joined: 03/27/07	Follow up on raising motor: my son took the boat and ran it. He said it ran great. Thanks for all the help from this site.