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

[JL8Jeff]

@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.

My boat would start to porpoise at higher speeds so I put the wedges on and it fixed the porpoising.

 

[LarryMc]

I can see that they aren't bent with the new photos that you posted. Stinkfoot's suggestion might be worth a try.

 

[stinkfoot]

Might be possible to fabricate something that was adjustable rather than buying actual trim tabs....

 

[rotus623]

Yea I don't want to put actual trim tabs on because they will dig a little deeper down than I want. I think a bendable set of removable aluminum plates bolted in would do well.

I am having a hard time still, understanding how this boat that is designed to run in inches of water is running in 10"+. It would seem something extremely fundamentally wrong is going on. I need to inspect the liner clearance also. I also wonder if adding an extra 50-60lbs for a 90/65 2 stroke jet will help or hurt me.

I also think that the 48" bottom is part of the culprit. Would float pods help at all? I know they are more for static displacement...... wheels are just turning here guys. I have set up a lot of boats but not many jets with marginal power. Transom tag says max motor is 90/65 jet.

 

[stinkfoot]

I thought about float pods for your problem. I have a buddy with a Wooldridge with a 115/80 and another with a G3 with a 60/40. I noticed when the Wooly slows down so the G3 can keep up his *** sits really deep and bow way up even though he is still planing....

 

[rotus623]

That's good info! That backs up what Larry was saying earlier. Just because you are on plane doesn't mean you have enough oomph to get that tail end up and out of the water. These slick bottoms have a lot of drag due to surface tension. Which also adds to the sluggishness.

My last boat was the same way. Was a 16' all welded jon and had a 25/20 tiller steer on the back. Got in plane pretty well but tail end just set low. I guarantee that light boat would have loved a 50/35 on it. But the hull wasn't solid enough for me. I just don't want to split a hull wide open and hurt someone. I don't know the upper James as well as I would like to so I like the idea of a tank to learn.

 

[stinkfoot]

See you posted on meanchicken. Probably the best place to get advice. I am arrgh! on there....

 

[rotus623]

Ok bud cool. Yea I know you and Jeff are on there, possibly Larry too? I am just scrounging for ideas before I yank this engine off. I'd hate to do it if I don't need to.

 

[LarryMc]

I'm on meanchicken now. :mrgreen: Didn't even know it existed until I saw stinkfoot's post a few minutes ago.

 

[stinkfoot]

I'm on meanchicken now. :mrgreen: Didn't even know it existed until I saw stinkfoot's post a few minutes ago.

People from all over on there. Some interesting stuff to read. I like it when the NZ boys show off their stuff and there was an awesome jet build from Africa. Funnily enough it was someone on Meanchicken that put me on to Tinboats..... 8)

 

[rotus623]

Them boys over there make me want to scrap the outboard jet deal and go inboard jet

 

[stinkfoot]

https://www.jetstreamboats.com/ This guy is just up the road from me. If you can weld you can pick up a kit for around US$2K.

 

[rotus623]

Man those things are sweet!! You could go anywhere in them!

 

[stinkfoot]

Man those things are sweet!! You could go anywhere in them!

There are a couple of build threads on meanchicken. I believe the owner is also on there.

 

[handyandy]

The tunnel is slowing you down for sure makes the back end/stern draft more water. It helps protect the shoe some but I always question how much good they do if they get the shoe 2-3" higher but makes the stern sit 1-3" lower causing more drag and reduced speed. The only way you will get much better performance with the combo is for starters make sure everything in the engine is up to snuff, like how sharp is the impeller, whats the impeller to liner clearance, what rpm is it running wide open. They changed the stainless impeller design that mercury sells those engines with now to help the four strokes get in there peak rpm range if you have the old style impeller it's better suited to two strokes, I'd be glad to buy it off you if you have the old style. Heck I'd buy you a new style one for a old style if it's in good shape. So check your wide open rpm. You could ;sand and polish the impeller, intake, and pump to for some performance gains but it's a lot of work for little gain that ultimately can get ruined by ingesting some gravel on accident. With that said sanding out real rough spots and getting everything at least smoother than the factories rather rough castings helps some. Three do anything you can to lighten the boat up. If you can get away with one trolling motor battery than lose a battery, maybe the flotation foam is water logged and needs to be replaced. Losing weight out of the boat will give you the most gain. Adding some flotation pods to the back won't help top speed but could help hole shot and resting draft. Ultimately pods and a 90/65 would give you the best results. At the end of the day it seems like flat tunnel hulls in this size range 16-18ft are just hard to make fast equivalent flat bottoms just run faster cause they don't have as much drag.

 

[rotus623]

Thanks for the in depth reply.

Yea those tunnels really up the drag and cut back on speed, that's for sure. That's the way they do it in the James though. I, personally,am happy sacrificing some speed/performance for the protection of a jet tunnel and UHMW plastic.(I am not getting snippy, just being honest) I split an .080 gauge hull right down the middle in april last year. I have also smacked the living tar out of my foot idling around and even drifting (last motor was not power trim.) Running new spots on the river can be a dangerous feat!! The ironic part is that you want to run it slowly to learn it, but can't because you are drafting too much water while at idle.

As far as impellers go, this one actually looks so clean I questioned if it was new!! I am going to inspect the liner clearance, as I suspect that the clearance may be too great. The guy who had the boat before me put in a new waterpump, and I doubt he tried moving the washers around. I will pull it in the next few days and get you a part number and take some pics. If you like what you see, I will take you up on your offer, and will gladly trade the old style for a new style. (The motor is an '07, so not sure when they changed the impellers over.)

Here is a video of a tunnel rhino running with a small tohatsu jet. I am pretty sure this looks very similar to how my hull looks while under way. https://www.youtube.com/watch?v=T1BKaexw7kc

 

[rotus623]

Oh, also, I called specialty mfg, and talked to the lady up front. She has always been very helpful to me. Anyways, I told her what pump I had on my rig (AGL-44) and she told me that the impeller was exactly the same as the 60/40 2 stroke, a 6 7/8" 3 blade. I have heard that some motors use a different impeller for 4s and 2s, but why wouldn't she know if this was the case? Seems strange....

 

[LarryMc]

It sounds like your motor has been converted from a prop to a jet. The AGL-44 is a unit designed to convert a long (20") shaft prop lower 4 stroke 60 HP motor to a 60/40 jet. It comes with an aluminum impeller that is the same as the one on the 2 stroke kits that Outboard jets sell. The aluminum impeller is part # 106.23. You should take yours off and see what the number is. The stainless factory impeller is part # 855708T60.

The pump on my motor, a factory jet manufactured in 2016, is an AGM. It came with a stainless 3 bladed impeller which has the trailing edge cut back to allow the 4 strokes to rev up a little higher than they will with the 2 stroke stainless impeller which has not been cut back.

 

[rotus623]

Man you guys are really on the ball here.

So, the motor serial number brings us to a 60hp EFI. No jet under parts breakdown. Plus the sticker said 60 on the cowling. So the motor has certainly been converted. Here's the fun part. The serial number on the pump is an AG, which was the same one on my short shaft 2 stroke 60/40. So I am guessing the guy who converted this just changed out the driveshaft for a 20".

All that being discovered, I am nearly positive that my impeller is the old 2 stroke style. (I guess that means it's aluminum?) how many rpms does one typically gain by moving to the stainless back cut impeller? What do one of those bad boys run new?

 

[rotus623]

Now what I am wondering is if the 2 stroke pump is hindering my performance. It looks like the liner on the 4 stroke is much smaller, and the foot is smaller also.