20' Master Angler, Yamaha 115 four stroke
 

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.

Weight of Merc 150 v-6
 

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.

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.

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

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

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?

115
 

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.

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.

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

I still love my Merc 115 two stroke DFI. Great mileage and a top end of 41mph on my twenty. I also love the quietness of four strokes.

Michael

Hi Capt5245, I have a 71 CC custom open fisherman, and powered it with a Merc 225 Opti. This is a lot of power for this boat, but it will easily handle it, and when I retire this motor I will go with their 250HP Opti. I prefer the bigger motors encase I want to carry a lot of weight in the boat, which puts little to no strain on the motor, and also gives me the extra power and speed if necessary. My boat will run all day, on 25 or so gallons of gas, turning 3000 to 4200 rpm's. My beliefs in motor size is simple, if I need the extra power it's their, and if I under power the boat, I can't. If I were you, I would go with at least a 150HP motor, more likely a 200HP motor, you won't regret it.

I have a F100 on a 1975 20 master angler with a giant T-top. I am happy with it. I think a 115 would be great.

Thank you for the input!

90 optimax on 70's safari, no speed demon but moves 20 to 23 fine. How fast do you need to go?

90's
 

But you run very light don't you?
Like this.......

go with a 150!...i had a yamaha 115 and it has no torque! I went with an e-tech.

ETEC Torque
 

Yes, the ETECs have strong torque, particularly at lower rpm. They win the “tractor-pulls” versus identical hulls. While probably not a problem for most CSC users, my G1 ETEC 150 HO on my 20’ Seafari was too torquey. It would not hold a steady wakeboard speed of about 18mph. The old V6 Merc 150 required some throttle manipulation, but would hold speed. I solved the ETEC issue with a 5 blade High Five prop and a PerfectPass GPS speed control. After spending about $1200 and lots of hours to figure how to adapt it to the ETEC, I have a tow machine that keeps the driver and the rider happy! BTW the ETEC is quick starting and much quieter.

Did you re-power with the Yammie? Just thinking (dangerous, I know), I believe that newer Merc 115 2.1 L would allow you to keep your old controls, and save you a couple grand on the motor price, too. with nearly 20% more displacement, pretty sure it out performs the Yammie and runs only 365 lbs or so. For performance perspective check out Bigshrimpin's performance - he just re-powered his 23 with a late model 150 Merc 4-S and is producing some very impressive numbers. Which ever color you choose, good luck with your purchase - modern motors are sweet!
Here's bit of that thread:
http://www.classicseacraft.com/commu...t=28644&page=3
check his metered performance on page 9.

Thank you! Have not done anything yet. Going to finance the work on the new boat with the proceeds of the sale on the old boat.