4 stroke 60/40 on 1648 River Rhino with UHMW??

[rotus623]

Hey guys I was working on a jet boat project and ended up selling my motor and going to sell the boat separately.
I realized that I was going to spend about 7-8k total plus lots of time and I have found some nice rigs up and down the east coast for around the same price.

Anyways, I found a 1648 river rhino with 4 stroke 60/40 merc and uhmw on the bottom, up in Pennsylvania. The boat is .125 gauge all around. Anyways, as I am thinking about it I feel like this thing might be named the "sea slug" and that may be why the guy is selling it. I am thinking with the weight of the 4 stroke and UHMW, and narrow bottom of 48", we have a sluggish combo. What do you guys think?

 

[LarryMc]

Did you see this Rhino with a 2 stroke 60/40 made by James River Jets?
https://richmond.craigslist.org/boa/5949567631.html
I fished a couple of times with a guy that had one almost identical with the one shown here. It was a real nice boat with lots of storage and Stick Steering which I really like. It ran pretty good, although not quite as fast or as quick to get on plane as my Lowe when I had the 2 stroke 60/40 on it. He had UHMW put on it after he had owned it for a while. He told me that the UHMW really hurt the performance, but I never fished in it after the UHMW was installed so I can't say how much performance loss there actually was.

I wouldn't want to speculate why the guy with the boat you described wants to sell it, but judging from my experience with re-powering my boat with a Mercury 4 stroke 40 jet, I would guess that the performance of his boat with the combination of a 4 stroke 40 jet, a .i25" hull and an UHMW bottom would leave a lot to be desired. That said, the only way to actually know what the boat will do is to drive it, so that would be my suggestion before deciding whether or not to buy it.

 

[rotus623]

Thanks for the in depth reply. Hull is similar to what you posted, but with a 4 stroke engine. I am wondering, what did you notice performance wise when you moved from a 2strok to 4 stroke 60/40?

 

[LarryMc]

I lost 2-3 MPH of top speed running in still water and the hole shot really suffered after the switch. I would estimate that it takes close to double the distance to get on plane with the 4 stroke as it did the 2 stroke. The lower top speed doesn't bother me nearly as much as the increased distance required to get on plane. There are times when running a jet that you need to get on plane quickly in shallow water in order to avoid hitting bottom with the jet foot. The 4 stroke just doesn't cut it in a situation like that.

Check out the thread link below for a more comprehensive discussion of the difference between the two motors.
https://www.tinboats.net/forum/viewtopic.php?f=85&t=41247

 

[rotus623]

I would estimate that it takes close to double the distance to get on plane with the 4 stroke as it did the 2 stroke.

WOW!! See I hear rumors about this all the time, but it's nice to hear it straight from the horses mouth. I do love the idling properties of 4 strokes, and how quiet they are when trolling around. I do a lot of idling where I fish, and much of the time I am running through new places. BUT, that being said there are places where a fast hole shot is required. Especially in late August early September when the water gets real low.

So on a narrow bottom (48") with UHMW, .125 hull, and 4 stroke engine, I think I am starting to see why this guy is selling this rig. Probably really is a "sea slug."

 

[rotus623]

Ok fellas so I took her for a test run today. Checked compression and we were looking at 180psi across the bboard cold. She fired right up and idled perfectly. Looked great under the hood and had a good amount of power.

So the boat is .125 all around. It has 1/8" UHMW (30lbsof weight according to Jim Starkey) and a tunnel. Three batteries and a full 12 gallon fuel tank. One 200lb guy and one 150lb guy. Honestly the hole shot was pretty good all things considered. She got on plane in about 2 boat lengths. Stayed on plane easily. There were two issues that I noticed. One was top speed upriver was only 23 and down river 25. The other issue is that the tail end rode heavy. Ran maybe 10" deep in the back on plane. I was hoping for much better than that.

The start battery and gas tank was in the rear, about 120lbs total. The 4 stroke motor weighs 267lbs.

I was thinking of starting by moving the tank and battery up. If that doesn't work maybe I need to sell the motor and get a 90/65 2 stroke? The motor is clean and I'm sure I can get $4000-4500 for it in a couple Weeks.

Price was great!! So I did purchase it. What you guys think I should do to get better performance?

 

[rotus623]

 

[JL8Jeff]

That speed might be right for the 4 stroke, that boat looks kind of heavy compared to my 1652 Lowe.

 

[stinkfoot]

I would definitely try shifting some weight around to get the boat more level. Makes a huge difference on my 16 foot jet jon.

 

[rotus623]

Cool man, I will try shifting some weight. I also need to inspect my impeller clearance.

 

[rotus623]

@JL8Jeff hey bud was wondering. How did you know you needed to wedge your transom? I feel like tucking the foot in will help some, although the transom angle is built
For yet motors on the rhino jets.

 

[LarryMc]

With a bow mount trolling motor, two TM batteries up front and the driver also up front, I doubt that the weight distribution is very far off. How does it float when not under power?

Have any idea what the Wide Open Throttle RPM is?

 

[rotus623]

Hmmm,

Don't have a tach on it yet, but I have a video I will try and post. Motor sounds about right, maybe around 5000rpms or so.

It floats really well while not under power, maybe 5-6".

 

[rotus623]

Here's a vid of her runnin to give you an idea of WOT rpms.

https://m.youtube.com/watch?feature=youtu.be&v=SXL5DXoyLSY

 

[LarryMc]

Hmmm,

Don't have a tach on it yet, but I have a video I will try and post. Motor sounds about right, maybe around 5000rpms or so.

It floats really well while not under power, maybe 5-6".

Does it float level from stern to bow? If so, your weight distribution is good. A jet boat that runs with the stern low and the bow high is often a sign that the boat is under-powered. I honestly doubt, given the construction of the boat that you have, that you will be able to improve the performance with the 4 stroke Mercury 40 Jet. If you do succeed in getting the bow to run lower, it will probably just plow through the water and will actually reduce your top speed.

 

[rotus623]

Not sure how she looks in the water at rest, but the waterline suggests it is relatively balanced. I don't feel like the boat has its nose in the sky when it is running, just that the tail end sets too low. It has plenty of power to get on plane, and you can throttle back 1/4 or so and it will stay planed out. This is one heavy boat for sure though

 

[LarryMc]

A suggestion that might help raise the stern. Try bending the trim tabs down. The one on the starboard side in the photo of your motor looks like it's bent up.

 

[rotus623]

So I think I hit the jackpot in one aspect. I measured the thickness of thenbottom and its .190 gauge!! Man this thing is a tank!! Just adding to more reasons why the 60/40 is an ad choice on her, not that it won't do the job

Anyways, I looked at the "trim" tabs oming off the back and they aren't bent at all. The issue is that they are very thick and are welded to the water drains and the tracking channel underneath. I think trying to bend these will be a lost cause and nearly impossible short of cutting a notch in them on the outer side of the tracking channel. That thing is covered with uhmw too!!

 

[stinkfoot]

You could bend some thinner aluminum and bolt it on to what you have though.

 

[rotus623]

That's a great idea stinkfoot!!! That will allow me to just take em off if i don't like em.
Trim tabs really helped my other boat. It may be worth a shot!