What new outboards are suitable for 18' tunnel hulls?

**deckofficer** · 07-23-2018, 12:35 PM

When a buyer buys a new STV or Quarter Shot, what new outboard does he choose? If these hulls can handle the weight of a 300R at over 500 lbs I guess that would be the motor to go with, but can they? I always thought the right outboard would be the Mercury 2.5 280 hp at 375 lbs. Can anyone shed some light on this for me and possibly others wanting a new 18' tunnel boat with a new motor with warranty?

**specboatops** · 07-23-2018, 12:37 PM

Most of the time, not always, they have a motor already.

**deckofficer** · 07-23-2018, 12:41 PM

So I guess that is why I see so many 18' tunnels being sold without engines? If they have a 260 or 280 they are going to keep this no longer produced motor because there isn't a suitable replacement?

**pkstv** · 07-23-2018, 01:37 PM

Originally Posted by deckofficer

So I guess that is why I see so many 18' tunnels being sold without engines? If they have a 260 or 280 they are going to keep this no longer produced motor because there isn't a suitable replacement?

You are correct . Mercury still makes a 2.5 promax block 225 hp to which a lot of 260 parts work to make a nice new motor so to speak that will last a long time with the steel sleeve cylinder walls . There’s still tons of mercury motor parts out there so the 18-19 ft tunnel boat market maybe slo , but it will continue on for the true drag race or top end enthusiasts!

**marks86** · 07-23-2018, 01:42 PM

I know mercury used to make small batches of the 2.5 drag motors, just for the racers. when did that stop?

**deckofficer** · 07-23-2018, 02:04 PM

Thanks for the input. Lets say I'd be content with a 85 mph ride that could be attained with the Mercury 115 hp offering. With that motor's 2.07 to 1 gear case that would require a prop of at least a pitch of 32". I can't find that pitch for that motor, they only go up to 21". What I'm getting at is I want everything new, not having to scrounge for used motors or motor parts. Besides with the weight of the 115 hp being 16 lbs lighter than a 2.5 280 at 375 lbs it should still have a decent hole shot with outstanding cruise speed (50 mph) fuel economy. The lake that would be home to a new boat has speed limits, so triple digits speeds aren't needed to hang with the pack like at Parker.

**mach351** · 07-23-2018, 03:27 PM

If triple digits aren’t what you’re looking for, then why go with an stv? Listen, I love my boat, but there’s really only one thing it does well - goes really fast with just me in it. There’s a ton of other boats that will do what you’re looking for.

**allstock** · 07-23-2018, 03:41 PM

Lots of 18' tunnels and vees out there with modern 500lb motors on them running just fine and fast! Edwards perso's YT has a 300 hpdi yamaha on it, many STV's and Mirages running around with 3.0 liters on them as well. 375lb motors are obsolete unfortunetly.

**pearlriverrat** · 07-23-2018, 03:51 PM

There are quite a few running around with all varieties of 300 Mercury. I don't understand your concern about weight of the new Mercs.

My question is, as mentioned above, what exactly are you looking for?

STVs hate the big wakes that come with today's ski/wake boats, plus, I don't think you would get that 85 mph ride with a 115 as easily as you are thinking. IMO, if you are just looking for a lake boat, but want a sporty one, go Allison and use whatever power you desire. Maybe with the XB02, you might be satisfied with that 115.

**deckofficer** · 07-23-2018, 04:10 PM

Originally Posted by mach351

If triple digits aren’t what you’re looking for, then why go with an stv? Listen, I love my boat, but there’s really only one thing it does well - goes really fast with just me in it. There’s a ton of other boats that will do what you’re looking for.

As you being an owner of a STV I respect your point of view. I believe the STV has more going for it other than 120 mph top speed. Its hull design has a minimum of wetted surface when air is packing in and lifting the hull up, thus much more fuel efficient than a Vee hull. Also less pounding in small chop. The light weight gives it better power to weight ratios for whatever power is hanging on the transom, hence better overall performance and hole shot. A rough rule of thumb is it takes 8 times the hp to double the speed. On a hull as light and efficient as a typical 18' tunnel can hit 120 mph on 300 hp, then 60 mph should be attainable with around 40 hp. I want a light boat that is efficient, and 18' tunnel hulls fill that bill. While 115 hp won't make me on the par for performance with you and the Parker crowd, for the lake that will be home port it might be top dog. On hole shot alone, the typical ski or wakeboard boat tipping the scales at 2+ tons and 400 hp would be no match for a 18' tunnel at 1/5 the weight with just 115 hp on tap.

**deckofficer** · 07-23-2018, 04:15 PM

allstock,

That is what I wanted to hear. So a Quartershot with a 300R is an acceptable combo? I've been under the false impression that these boats recommend less than 400 lb outboards.

**allstock** · 07-23-2018, 04:58 PM

Originally Posted by deckofficer

allstock,

That is what I wanted to hear. So a Quartershot with a 300R is an acceptable combo? I've been under the false impression that these boats recommend less than 400 lb outboards.

It should be great! 500 lb motors are here to stay. And yes I would say most every high performance boat models out there have had a modern outboard bolted on.

**BUZZIN' DOZEN** · 07-23-2018, 05:24 PM

**Brad Zastrow** · 07-23-2018, 05:30 PM

How many new 18' STV's are built each year?

**home made tunnel** · 07-23-2018, 05:52 PM

Originally Posted by deckofficer

As you being an owner of a STV I respect your point of view. I believe the STV has more going for it other than 120 mph top speed. Its hull design has a minimum of wetted surface when air is packing in and lifting the hull up, thus much more fuel efficient than a Vee hull. Also less pounding in small chop. The light weight gives it better power to weight ratios for whatever power is hanging on the transom, hence better overall performance and hole shot. A rough rule of thumb is it takes 8 times the hp to double the speed. On a hull as light and efficient as a typical 18' tunnel can hit 120 mph on 300 hp, then 60 mph should be attainable with around 40 hp. I want a light boat that is efficient, and 18' tunnel hulls fill that bill. While 115 hp won't make me on the par for performance with you and the Parker crowd, for the lake that will be home port it might be top dog. On hole shot alone, the typical ski or wakeboard boat tipping the scales at 2+ tons and 400 hp would be no match for a 18' tunnel at 1/5 the weight with just 115 hp on tap.

LOL at going 60mph with 40hp. Good luck. My chitty bayliner won't hit 60 with 120hp!