Engine Choice Yamaha V MAX SHO 115 or Mercury 115 Pro XS

[Hypalon]

I have an 18’ (550) Deltabay RIB, which is exactly the same as the 3D Tender Patrol 550. I fitted the boat with a Suzuki DF115B, and at 6,000 RPM with one person and little fuel, I have reached 45 MPH. In real-world conditions, with my son onboard and 100L of fuel, I can achieve 41 MPH at 6,000 RPM.

We fish an island about an hour away and would like to get there faster, so I am considering swapping the Suzuki DF115B for either a Yamaha V MAX SHO 115 or a Mercury 115 Pro XS. I have read that both of these engines are considerably faster than my Suzuki. Honestly, I thought that top speed was the same across all 115HP engines, which is why I originally chose the Suzuki, knowing it to be very reliable.

I am leaning toward the Mercury 115 Pro XS. I see that it offers a Command Thrust (CT) gearcase option for heavier boats, but I suppose my boat wouldn’t really benefit from that.

I should have asked these questions before getting the Suzuki, but now I’m thinking about repowering. I’m not sure whether to go with the Yamaha V MAX SHO 115 or the Mercury 115 Pro XS, and I wanted to reach out to the RIB community for input.
I would appreciate any input.

[beamishken]

Originally Posted by Hypalon

I have an 18’ (550) Deltabay RIB, which is exactly the same as the 3D Tender Patrol 550. I fitted the boat with a Suzuki DF115B, and at 6,000 RPM with one person and little fuel, I have reached 45 MPH. In real-world conditions, with my son onboard and 100L of fuel, I can achieve 41 MPH at 6,000 RPM.

We fish an island about an hour away and would like to get there faster, so I am considering swapping the Suzuki DF115B for either a Yamaha V MAX SHO 115 or a Mercury 115 Pro XS. I have read that both of these engines are considerably faster than my Suzuki. Honestly, I thought that top speed was the same across all 115HP engines, which is why I originally chose the Suzuki, knowing it to be very reliable.

I am leaning toward the Mercury 115 Pro XS. I see that it offers a Command Thrust (CT) gearcase option for heavier boats, but I suppose my boat wouldn’t really benefit from that.

I should have asked these questions before getting the Suzuki, but now I’m thinking about repowering. I’m not sure whether to go with the Yamaha V MAX SHO 115 or the Mercury 115 Pro XS, and I wanted to reach out to the RIB community for input.
I would appreciate any input.

Unless your due to repower for other reasons then your going to spend an awful lot of money for a very small gain, admittedly some engines can be faster than others in a particular hp however the difference is prety negligible probably only 2 or 3 kts if you realy want go a meaningful amount faster you need to increase hp

[Hypalon]

Thank you for your opinion. I was reading that the Yamaha V MAX SHO 115 and the Mercury 115 Pro XS can be as much as 10 MPH faster than the Suzuki. I was thinking that if I could get an extra 10 MPH, that would actually be significant. Reading all the marketing materials about Mercury got me excited. However, what you wrote made me think more critically — so I started digging deeper (thank you, by the way).

I ended up spending the last two hours on GPT-4o, asking it to calculate the anticipated top speed on the 3D Tender with the Mercury. It compared real-world boat types and then ran a technical hydrodynamic calculation based on hull drag, boat weight, and engine power to estimate top speed. Because a RIB has more hull drag than a bass boat, even with the same engine, it realistically tops out around 40–43 mph instead of 50+ mph like lighter, flatter bass boats. It turns out that the top speeds I’ve been reading about are all based on bass boats, not RIBs.

So for now, I’m going to take your advice unless I hear from someone who has a boat like mine — or a similar Zodiac Open 5.5 — with a Mercury 115 Pro XS, and is actually hitting over 50 MPH. Thanks again for your input!

[Playtime]

I had a Ribeye a600 with a Yamaha f115 2003 and repowered with a sho 115 and saw about a 4 mph increase but was more punchy lower down. I can’t remember if we used the same pitch/size prop though.
Hope this helps

[ThundercatRob]

Are you planning to run your engine flat out for an hour each way to the island?

I assume it’s correctly propped and you have checked that?

[spartacus]

Not much to add. Be cheaper relocating home, than upgrading the outboard. 40mph to get to fishing grounds. Take a chill pill. The fish will still be there. Leave earlier in the morning.

[beerbelly]

i have a humber destroyer 5.5 with a mercury 115 CT and using a 19p 4 blade stainless prop i get a tadge over 40mph at 6000rpm .i think what your seeing is par for the course with a 5.5 rib with 115 horses

[Hypalon]

On the way out to the islands, I typically run at wide-open throttle (WOT) at 6,000 RPM and reach about 40 MPH. On the way back, however, there’s usually more chop as the winds increase, making it more difficult to maintain WOT. I’m currently running a 14x22 RH PowerTech 3-blade stainless steel prop, and I’ve adjusted the outboard so that the cavitation plate is level with the boat's bottom at the keel.

When the boat is low on fuel, and I am alone with minimal gear, I have reached 45 MPH on the lake. It’s a bit more difficult to hit those speeds in the ocean due to the chop, and I’m generally with my son and carrying a full tank of fuel when we head out to sea. From what I understand, achieving 40–45 MPH with my Suzuki DF115B is considered respectable performance for a RIB boat, so I believe I have the setup tuned about as well as it can be.

[Hypalon]

Thank you for your input. You have the CT version, so I assume you can run a wider variety of propellers. I have been reading that for lighter boats, the Command Thrust (CT) option isn’t always ideal, as it can sacrifice some top speed in favor of better hole shot and low-end power.

I do think you’re right. After spending the weekend reading and using GPT-4o to help estimate the potential top speed of the 3D Tender equipped with the Mercury, it analyzed real-world comparisons between different boat types and performed a detailed hydrodynamic calculation, factoring in hull resistance, overall weight, and engine output. Since RIBs create more drag in the water than sleek, flat-bottomed bass boats, even when powered by the same motor, the realistic top speed is closer to 40–43 mph rather than the 50+ mph often seen with lighter, faster boats.

If I knew for certain that my boat would reach 50+ MPH with the Mercury, I would make the swap. However, after a lot of reading, I'm not so sure I would see a significant improvement. To spend thousands of dollars to “upgrade” and only see a marginal gain would leave me feeling a bit foolish—especially considering I’d be giving up the well-known reliability of Suzuki for only a slight performance increase with the Mercury.

[Hypalon]

Originally Posted by spartacus

Not much to add. Be cheaper relocating home, than upgrading the outboard. 40mph to get to fishing grounds. Take a chill pill. The fish will still be there. Leave earlier in the morning.

You’re correct! That said, the culture in America is quite different from that in the UK. Here, it's common to see 700-horsepower Dodge Hellcats on the roads, and even among EVs, the Tesla Model S Plaid—which can achieve 0–60 mph in just 2.1 seconds—is a regular sight on the freeway. On the water, I can't even count how many boats I see equipped with twin or even quad 600-horsepower Mercury Verados.

In San Diego, where I’m located, we actually don’t see many RIB boats unless they belong to the Navy, Border Patrol, or USCG. They primarily operate Metal Shark, Willard Marine, or Zodiac Mil-Pro boats, and they usually cruise around at over 50 mph. Every time we're out on the water, we’ll see a Navy RIB flying by us at 50+ mph, often with a .50 caliber weapon mounted on the bow—which is both intimidating and pretty cool at the same time.

[69cmw]

I had a Humber Destroyer 5.5 with a new Yam 115hp, running a 18” st steel prop, 6100-6200 revs was getting 48-49 mph.
That was 1 up

[Hypalon]

Originally Posted by 69cmw

I had a Humber Destroyer 5.5 with a new Yam 115hp, running a 18” st steel prop, 6100-6200 revs was getting 48-49 mph.
That was 1 up

That's impressive. Was that the V MAX SHO 115

[Steve509926]

Originally Posted by Hypalon

You’re correct! That said, the culture in America is quite different from that in the UK. Here, it's common to see 700-horsepower Dodge Hellcats on the roads, and even among EVs, the Tesla Model S Plaid—which can achieve 0–60 mph in just 2.1 seconds—is a regular sight on the freeway. On the water, I can't even count how many boats I see equipped with twin or even quad 600-horsepower Mercury Verados.

So break the chain and chill

[beamishken]

If your engine is level with the hull your engine is too deep lift it a hole at a time until you experience excess ventilation then drop back one hole & you'll be about right, you'll probably gain a kt or two