20' Master Angler, Yamaha 115 four stroke

[Cptn5245]

I am considering purchasing a 20' Seacraft built in 2004. It currently has a 150 Merc 2 stroke on it. I'd like to repower it in the future with a Yamaha 115 four stroke (366 lbs). Does any body have this configuration? How can I estimate performance?

Having read many of the threads here, I recognize the issues with heavier, higher hp motors. With me weighing in at 300 lbs, it appears that I have to be cognizant of the weight of the motor to minimize wet feet at the transom.

Any insight would be appreciated.

[Capt Terry]

By memory I think my 1985 Merc v-6 150 HP weighed 375#. Therefore I'd think you are already in that ballpark. Mine is a1976 Seafari which carries more weight forward and has the raised deck as yours probably does. I generally left the plugs in the scuppers except when tied up to the dock. Mine is a 20" transom and there is not a lot of freeboard at the transom cutout with a 418# ETEC 150. Wet feet was only a problem with an aft load and in a Seafari no one sits forward of the helm.

[McGillicuddy]

Your 20' is a bit longer than the originals.
Also as Capt. Terry mention sole and transom were raised.

I think 366 lbs Yamaha is fine. Not sure of its gear ratio, but if 2:1 or so, a stern lifting 13-3/4 x 15 ought to give your best all around performance. Best hole shot, 12-15 mph plane, 4+ mpg at cruise and about 36 mph top end. I really like the Quicksilver Black Diamond in aluminum and PowerTech's MQF 3 blade. I believe they both have a smaller 4 blade variant of similar blade shape.

This will vary if Yamaha has gone to a 2.25:1 or more like Suzuki and others have done. That may enable more prop.

[Cptn5245]

Thanks for the information, it is greatly appreciated. Have a Happy New Year!

[Basketcase]

fyi the new yammie is 377lb and 1.8L but the Merc 115 is 363 and 2.1L of displacement.

[Cptn5245]

So I bought the boat and am very happy with it so far. Definitely want to re power with a 4 stroke motor. Had a conversation with the local merc dealer. He felt the 115 hp was not enough power for the boat. I do see other boats that are heavier with 115 hp power. The conversation left me confused. Is anybody out there running the 20 foot Sea Craft with 115 hp? If so are you happy with the performance?

[Terry England]

Tom, you need to determine your "need for speed?". If you don't have a big Tee top with an electronics box and just a Bimini you will probably see 36 MPH with a 4000 rpm 24 MPH cruise with the 115. If you are trying to beat Donald Campbell's records you will need a lot more "juice". If you normally cruise at 20, don't run with a big load and don't want to spill you beer, you'll be OK with a 90. Just figure out what you are doing with the boat. They typically "push" pretty easy and were designed when the biggest outboards were Mark 78 Merc's.

[Bushwacker]

Originally Posted by Cptn5245

. . . Had a conversation with the local merc dealer. He felt the 115 hp was not enough power for the boat. I do see other boats that are heavier with 115 hp power. The conversation left me confused. . . .

That's because he's probably used to dealing with modern 8' beam 20' boats built for 4S motors that are far less efficient than the VDH hull of a 20' SeaCraft that was built for motors of 300 lbs or less! They were often sold new with 85-115 hp motors back in the late 60's/early 70's!

[DonV]

Originally Posted by Bushwacker

That's because he's probably used to dealing with modern 8' beam 20' boats built for 4S motors that are far less efficient than the VDH hull of a 20' SeaCraft that was built for motors of 300 lbs or less! They were often sold new with 85-115 hp motors back in the late 60's/early 70's!

And don't forget, those motors were rated at the power head. Today's are rated at the prop.

[Cptn5245]

Thank you gentlemen! There is no need for speed for me.