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Old 12-23-2019, 11:54 AM   #1
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Dinghy power results (with a surprise twist!)

Greetings all! This is a follow up thread to one I had posted back in March. The TLDR is I was asking about power options for a yet to be purchased dinghy. As usual, you all brought your questions and opinions, always thankful for that!

I had meant to get to this post this last summer, but life and boating happened. Now it's cold, work slowed a bit, so here I am!

Here's the link to the old thread : Dinghy power thoughts

BUT...don't spend too much time reading that. This is about results...with a twist!

I ended up purchasing a Highfield 310 Classic dinghy. I also ordered a 20HP Mercury 4-stroke EFI outboard. The big debate for me at purchase was the 15 vs the 20. It's the same engine, same weight, the 20 has a different computer and as the dealer described it "a 10 cent washer that allows more fuel to be burned" to make it a 20. Oh, and I think the 20 was $300 or so more.

I got the boat back in June after a few delays. I've got some video footage I'm meaning to post too about the dink itself, but overall, happy with the Highfield 310.

After the break in period, I wanted to get specific about some performance data with the setup. I used Navionics on my iphone for data. I picked a calm day, and while I'm on the St. Croix river up in Minnesota, I picked a larger pool with less current.

I'm about 250 lbs, I had the boat, 6 gals of gas, oars, seats, a few docklines, and a few "silver sissies" (Coors light) as fuel for myself.

After break in of about 10 hours. Apologies, the speeds are in MPH.
3/4 throttle - 17mph
Full throttle - 19.5mph

Not bad right? The setup seemed to be just great, and I had really no idea what to expect, but sounds decent right? NOW...THE TWIST!

About 2 weeks after this test, I get a call from the dealer. He's says he's really embarrassed, and is apologizing, not telling me why. Well then he tells me- " Say, that 20hp you have? It's actually a 15hp. The covers got mixed up in the shop". Wow ok!

After much more apologizing, he offers me I can keep the 15, he'll get me the right hood, and of course give me the $ difference. Or, I can come get the REAL 20hp. Well now I'm real curious. Sure it's another trip, and engine off, engine on...break in period again. So I decide I want to get the 20...with the option if I'm not happy, I get the 15 back. He agrees. So I do the swap.

Maybe the 15 was just fine...I feel like it was. But I'll always wonder. Same setup as before, same type of day. Maybe I brought 3 silver sissies with this time as a reward for all my hard work. But ok, here we go, the real 20 hp's data:

3/4 throttle: 20 mph
Full throttle: 26 mph

Nice surprise eh? I can say the 20 really zipped top end, and also seemed to get out of the hole and on plane quicker. I did run the 15 with my family in it, my petite wife, 2 kids (5 and 7) and it did ok. But same family load, even the kids commented how zippy it now was.

Those speeds were significant enough that I kept the 20. Seems like it was worth it!

I'm happy to answer any other questions about the setup. This spring, I'm going to do some longer fuel consumption runs, most of our stuff was short fun trips.

I do have to say the setup is fast, maybe a little too much for someone not ready for it? The Mercury setup is nice, you can tension the turning force of the engine itself, and the throttle tension. Also I've found that the tiller adjustment is awesome - You can angle it off to one side, really nice in this small boat so the tiller isn't in your stomach. The engine also has the shifter on the tiller (think sticking up like a gear shifter) and I wasn't sure about that, but it is real nice as slow speeds for docking, etc. Easy to be at idle speeds and go in and out of forward into neutral then reverse.

Anyway, hope this was informational. More to come if I can get my videos together!

MnCruiser
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Old 12-23-2019, 11:59 AM   #2
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Cool.


And who's the dealer? I wish all were like that.
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Old 12-23-2019, 12:06 PM   #3
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Cool.


And who's the dealer? I wish all were like that.


Great American Marine in Bloomington, MN. He deals exclusively in inflatables.
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Old 12-23-2019, 01:29 PM   #4
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Originally Posted by mncruiser View Post
Greetings all! This is a follow up thread to one I had posted back in March. The TLDR is I was asking about power options for a yet to be purchased dinghy. As usual, you all brought your questions and opinions, always thankful for that!

I had meant to get to this post this last summer, but life and boating happened. Now it's cold, work slowed a bit, so here I am!

Here's the link to the old thread : Dinghy power thoughts

BUT...don't spend too much time reading that. This is about results...with a twist!

I ended up purchasing a Highfield 310 Classic dinghy. I also ordered a 20HP Mercury 4-stroke EFI outboard. The big debate for me at purchase was the 15 vs the 20. It's the same engine, same weight, the 20 has a different computer and as the dealer described it "a 10 cent washer that allows more fuel to be burned" to make it a 20. Oh, and I think the 20 was $300 or so more.

I got the boat back in June after a few delays. I've got some video footage I'm meaning to post too about the dink itself, but overall, happy with the Highfield 310.

After the break in period, I wanted to get specific about some performance data with the setup. I used Navionics on my iphone for data. I picked a calm day, and while I'm on the St. Croix river up in Minnesota, I picked a larger pool with less current.

I'm about 250 lbs, I had the boat, 6 gals of gas, oars, seats, a few docklines, and a few "silver sissies" (Coors light) as fuel for myself.

After break in of about 10 hours. Apologies, the speeds are in MPH.
3/4 throttle - 17mph
Full throttle - 19.5mph

Not bad right? The setup seemed to be just great, and I had really no idea what to expect, but sounds decent right? NOW...THE TWIST!

About 2 weeks after this test, I get a call from the dealer. He's says he's really embarrassed, and is apologizing, not telling me why. Well then he tells me- " Say, that 20hp you have? It's actually a 15hp. The covers got mixed up in the shop". Wow ok!

After much more apologizing, he offers me I can keep the 15, he'll get me the right hood, and of course give me the $ difference. Or, I can come get the REAL 20hp. Well now I'm real curious. Sure it's another trip, and engine off, engine on...break in period again. So I decide I want to get the 20...with the option if I'm not happy, I get the 15 back. He agrees. So I do the swap.

Maybe the 15 was just fine...I feel like it was. But I'll always wonder. Same setup as before, same type of day. Maybe I brought 3 silver sissies with this time as a reward for all my hard work. But ok, here we go, the real 20 hp's data:

3/4 throttle: 20 mph
Full throttle: 26 mph

Nice surprise eh? I can say the 20 really zipped top end, and also seemed to get out of the hole and on plane quicker. I did run the 15 with my family in it, my petite wife, 2 kids (5 and 7) and it did ok. But same family load, even the kids commented how zippy it now was.

Those speeds were significant enough that I kept the 20. Seems like it was worth it!

I'm happy to answer any other questions about the setup. This spring, I'm going to do some longer fuel consumption runs, most of our stuff was short fun trips.

I do have to say the setup is fast, maybe a little too much for someone not ready for it? The Mercury setup is nice, you can tension the turning force of the engine itself, and the throttle tension. Also I've found that the tiller adjustment is awesome - You can angle it off to one side, really nice in this small boat so the tiller isn't in your stomach. The engine also has the shifter on the tiller (think sticking up like a gear shifter) and I wasn't sure about that, but it is real nice as slow speeds for docking, etc. Easy to be at idle speeds and go in and out of forward into neutral then reverse.

Anyway, hope this was informational. More to come if I can get my videos together!

MnCruiser
Great post...
Did you have a way to get the rpm of each engine at WOT?
Is there any way to tell if the speed is derived from the extra HP or just from the different prop and/or lower unit gear ratio? (or maybe some of each)
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Old 12-23-2019, 01:41 PM   #5
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Did both engines have the same prop pitch?
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Old 12-23-2019, 01:43 PM   #6
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Originally Posted by smitty477 View Post
Great post...

Did you have a way to get the rpm of each engine at WOT?

Is there any way to tell if the speed is derived from the extra HP or just from the different prop and/or lower unit gear ratio? (or maybe some of each)


I didn’t have a way to measure rpm, but my recollection was that the 20 was more “free revving” and definitely went to a little higher rpm.

It’s my understanding that the props and gear ratios are the same, the only difference was a small part in the fuel system and an different engine control computer. Everything else about the 15/20 is the same.
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Old 12-23-2019, 01:46 PM   #7
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I'm curious about how the dealer discovered the mistake in swapping engine covers. It's nice that he fessed up about their error and offered you some options to choose from to fix the issue.


I'm not familiar with the Highfield line of dinghies so I googled it and found a video from a Highfield dealer. It's a very nice looking dinghy; nicely appointed, nicely finished and looks like it would be comfy to ride in. One comment that surprised me is the guy doing the video said the 310 Classic is rated for a max of 15hp. They showed it with a Tohatsu motor on it.


I'd suggest checking your capacity plate to make sure you're legal. IMHO the difference between the 15 and the 20 is significant enough that I'd keep the 20 and go have fun.
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Old 12-23-2019, 01:59 PM   #8
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I'm curious about how the dealer discovered the mistake in swapping engine covers. It's nice that he fessed up about their error and offered you some options to choose from to fix the issue.


I'm not familiar with the Highfield line of dinghies so I googled it and found a video from a Highfield dealer. It's a very nice looking dinghy; nicely appointed, nicely finished and looks like it would be comfy to ride in. One comment that surprised me is the guy doing the video said the 310 Classic is rated for a max of 15hp. They showed it with a Tohatsu motor on it.


I'd suggest checking your capacity plate to make sure you're legal. IMHO the difference between the 15 and the 20 is significant enough that I'd keep the 20 and go have fun.
He found it trying to reconcile serial numbers during his inventory process. He had me down as having the 20, but had ordered a 15 at the same time and it was yet unsold. It's real good the other engine had not sold, the process would not have been so smooth swapping things back.

Can you imagine being the guy that got the 15 that was really a 20, and not wanting to give that back? Haha!

I actually enjoyed the process, was neat to have the chance to run both engines, and ultimately solidified my decision to choose the 20.

As for the capacity, it does indeed say 20hp. You can also see the capacities on the Highifield site: Classic 310 - Highfield Boats
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Old 12-23-2019, 02:08 PM   #9
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Great post...
Did you have a way to get the rpm of each engine at WOT?
Is there any way to tell if the speed is derived from the extra HP or just from the different prop and/or lower unit gear ratio? (or maybe some of each)
I did just look up the engine on Mercury's site, and indeed the gear ratio (2.15:1) is the same on both engines.

Link to engines here, click on the 15 EFI and 20 EFI to compare specs : https://www.mercurymarine.com/en/us/...troke/25-25hp/

What is interesting is both the 15 and 20 specs say the same max RPM range of 5700-6200. This is a guess, but maybe the 15 is limited to 5700, and the 20 is 6200? It certainly felt like it.

They don't list the prop pitches anywhere, at least not that I could find.
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Old 12-23-2019, 02:17 PM   #10
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Also, here's a good video from Mercury that shows the tiller handle adjustments and shifter. I was really sold on getting a Suzuki 20hp, but I have to admit the tiller thing was a winner for me for the Mercury. I can say in real use, it's adjustable features are pretty nice, especially in this small boat.

Video link showing the stuff I talked about :
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Old 12-23-2019, 04:20 PM   #11
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Hey all, I grabbed my videos back from June, and did a crappy fast editing job, and posted on youtube. I'm new at the video editing thing, and this one was filmed with an iphone. I just got a Gopro, and hoping to figure out how to edit better in the future. The video shows some of my comments, outfitting and a quick ride.

And yes, I was not wearing a life jacket, and in the first video of me running, the safety lanyard was not attached. Yes, I know, a huge safety issue. But I did notice it and attached it right after that clip. I've also invested in a nice comfy inflatable life jacket that attaches easily to the safety lanyard.

I've got no affiliation with Highfield or Mercury. Just a regular guy trying to give some content back to this forum!

The video: https://youtu.be/-9AT_aLplJU

Enjoy! And make fun of me...this is my first one!
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Old 12-23-2019, 06:53 PM   #12
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Awesome results. Not too many times you get what you think you bargained for and then get it swapped for better!

As for different top speeds, (WAG here) the lower speed with the 15 is demonstrating that 15hp is not enough power for the load. Add 5 hp and your outboard isn't overloaded, so you go faster.

I once tried a 15 on a 9' whaler, with just me (160lb) in it. I found out pretty quickly that 15hp was enough to go really, really fast. That same motor on my 11' inflatable wouldn't go nearly as fast.

On my present 12', with a speedo, 40 hp was getting me a steady 22mph until I bought a new prop without the shark bites. Top speed went up to 25.
Conclusion: everything you do will affect your top speed.
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Old 12-28-2019, 08:54 AM   #13
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26 mph is 22.6 knots.
I'm surprised it is not faster.

I can get to 25 knots (29+ mph) easy in my RIB with a 15 hp 2 stroke Yamaha.
A buddy with a 15 4 stroke Merc and same dink as mine raced and we were neck and neck.
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Old 12-28-2019, 09:05 AM   #14
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26 mph is 22.6 knots.
I'm surprised it is not faster.

I can get to 25 knots (29+ mph) easy in my RIB with a 15 hp 2 stroke Yamaha.
A buddy with a 15 4 stroke Merc and same dink as mine raced and we were neck and neck.
I get 23 mph in my 13.5 Del Quay Dory with a 9.8 Nissan two stroke on it, driving it by myself.
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Old 12-30-2019, 01:09 PM   #15
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Thanks for making this post OP, it is a good one and I enjoyed it. I'm looking hard at a Highfield 340 classic for our next dink, so this is very informative.



My current dink, a Caribe light 11 with a 20 hp Suzuki 4 stroke gets about 22 or 23 knots WOT under perfect conditions. It was a little faster before I put a whale tail on it which helped it in other ways. I think my dinghy is way heavier than its advertised weight though. It's hard as heck to drag around on the beach, even when I have my two athletic sons (21 and 17 YO) helping me.


I'm going to keep our current motor for the new dink, I'm hoping to not give up much speed, and from the sounds of your tests it seems reasonable that they will be about the same speed. I think the Highfields are lighter than even the Caribe lights, and my guess is the slightly longer waterline on the 340 will help performance some even on a plane.
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