Hello,
I own a 1983 Sea Sprite 889 Sandpiper. It is a typical 18' fiberglass bow rider. Its dry weight should be around 1200 lbs per the nada guides. We usually have about 18 gallons of gas, 2-3 people on board, 2 batteries, and about 120lbs of fishing/trolling gear and food/drink. The motor is a 1979 Mercury inline six, 90 hp, distributor-less ignition, serial 52999xx outboard. The boat came with a 13x19 aluminum 3 blade prop and at that time we managed 4300 rpm and about 32-33 mph on a gps at wot and trimmed up.
I bought a 13-1/4x17 3 blade hustler by turning point aluminum prop and installed it. This purchase was based on wot rpm specs of 4500-5000 in a clymer manual. The engine turned 4600 rpm and we made about 36 mph gps wot + trimmed with this prop.
Then I had some ignition trouble(posted in a different forum). I replaced the rectifier(shorted diode), the stator(leaking, corroded wires, crumbling insulation, and out of resistance spec), the trigger(out of resistance spec, crumbling insulation), and spark plugs. Actually I changed the plugs first but they weren't the problem(s).
After replacing all the parts, and adjusting sync and timing, the motor now turns 4800 rpm, at 38 mph gps.
In the other forum(repair) I was told that this engine should be turning 5200 - 5500 rpm. The only manual I have for this motor is a Clymer manual. It calls for 4500-5000 for 90hp, 5000-5500 for 115hp, and 5300-5800 for 140hp distributor-less six cylinder engines thru 1989. Does anyone know the actual Mercury spec? If my manual is correct, I am done prop testing and right in the rpm range I should be, if not I need an even smaller pitch prop. All of this is assuming the gear ratio is 1.7:1. I have not been able to find a reliable source for this spec either.
So does anyone know for sure if my motor's gear ratio is 1.7:1 and what Mercury says my wot rpm range should be?
Thank You in advance.
I own a 1983 Sea Sprite 889 Sandpiper. It is a typical 18' fiberglass bow rider. Its dry weight should be around 1200 lbs per the nada guides. We usually have about 18 gallons of gas, 2-3 people on board, 2 batteries, and about 120lbs of fishing/trolling gear and food/drink. The motor is a 1979 Mercury inline six, 90 hp, distributor-less ignition, serial 52999xx outboard. The boat came with a 13x19 aluminum 3 blade prop and at that time we managed 4300 rpm and about 32-33 mph on a gps at wot and trimmed up.
I bought a 13-1/4x17 3 blade hustler by turning point aluminum prop and installed it. This purchase was based on wot rpm specs of 4500-5000 in a clymer manual. The engine turned 4600 rpm and we made about 36 mph gps wot + trimmed with this prop.
Then I had some ignition trouble(posted in a different forum). I replaced the rectifier(shorted diode), the stator(leaking, corroded wires, crumbling insulation, and out of resistance spec), the trigger(out of resistance spec, crumbling insulation), and spark plugs. Actually I changed the plugs first but they weren't the problem(s).
After replacing all the parts, and adjusting sync and timing, the motor now turns 4800 rpm, at 38 mph gps.
In the other forum(repair) I was told that this engine should be turning 5200 - 5500 rpm. The only manual I have for this motor is a Clymer manual. It calls for 4500-5000 for 90hp, 5000-5500 for 115hp, and 5300-5800 for 140hp distributor-less six cylinder engines thru 1989. Does anyone know the actual Mercury spec? If my manual is correct, I am done prop testing and right in the rpm range I should be, if not I need an even smaller pitch prop. All of this is assuming the gear ratio is 1.7:1. I have not been able to find a reliable source for this spec either.
So does anyone know for sure if my motor's gear ratio is 1.7:1 and what Mercury says my wot rpm range should be?
Thank You in advance.