New to Jet Boats need advise please...

[HoytHunter69]

I have just recently got in to a jet rig and I need some help with a few things. first off I have a 1652 Lowe with a 90/65 Merc. It has a tunnel hull. Our rivers here are mostly sand and wood so I dont worry much about tearing the bottom up. A few things I have noticed about this boat is when I first got it it was a duck boat and wide open. I have since made it where I can fish tournaments out of it. so I have added a few things. 2 batterys, bait well I have plumbed as a livewell, trolling motor and electronics. speed wasnt really efected? it still runs 31-32 loaded.

Here are my problems. First it rides a little nose high and has from the day I got it? it will run as shallow as I need to go, and its really amazing at how shallow it will run. we pretty much say "if there is water showing, it will run it" but I'm wondering how to make it run flat?? should I move the three batterys all the way to the nose? two are pretty much up there, cranking battery is at the rear. console sits forward (i can provide a picture)

The other big thing is it hates a chop. I mean 4 inch chop and it blows out like crazy?? is this normal? if the wind gets up and I have to come out of the river to the big water to get back I can forget it??we tried letting my buddy sit on the front deck, and I think this helped some but its terrible in rough water. would pods help? also thought of stripping all the foam out in the back (which i think could be wet and holding water in the back ?)

any help would be appreciated. I dont know a whole lot about Jets??
Thanks in advance.

 

[Darkside]

Yes, you can shift weight and even the helm to balance the hull, but it may not improve speed any.

Chop issues are very likely due to the tunnel. Closing the tunnel can often help. Air ingesting in many tunnel hulls is a factor in choppy water. Would need to see how deep the tunnel is. Do you have any pictures of the set up?

 

[fender66]

The "nose high" thing could be a trim issue. If your trim get's too high....it will pull your nose up.

Jet's don't like chop all that much. Mine doesn't like it either. If you take a picture of your jet foot in relationship to the bottom of your boat....we might be able to suggest something that could help. Not sure, but it's worth a try.

 

[HoytHunter69]

yes I do. I will upload the boat first to give you an Idea, then a pic of the tunnel

 

[HoytHunter69]

The "nose high" thing could be a trim issue. If your trim get's too high....it will pull your nose up.

Jet's don't like chop all that much. Mine doesn't like it either. If you take a picture of your jet foot in relationship to the bottom of your boat....we might be able to suggest something that could help. Not sure, but it's worth a try.

Its been trim down the whole time. I cant trim up because water is coming over the splash guard in the back?? weird but I dont know? do you guys trim up like an outboard prop? or just run all the way down. let me up load a pic or two.

 

[HoytHunter69]

here is one pic

 

[HoytHunter69]

another

 

[HoytHunter69]

inside view...you can see the two flotation pods in side the rear. I'm wondering if there soaking wet and weighing down the rear? thought of digging it all out and making dry storage in the rear?

 

[HoytHunter69]

why does it ride nose up??

 

[fender66]

I still think it could be the trim. You might be able to raise the motor on the transom a bit too. Kind of hard for me to really tell from the pics. If it is a weight problem...meaning too much in the back, it would be easy enough to do a test and load the front of the boat down for a test.

 

[HoytHunter69]

I still think it could be the trim. You might be able to raise the motor on the transom a bit too. Kind of hard for me to really tell from the pics. If it is a weight problem...meaning too much in the back, it would be easy enough to do a test and load the front of the boat down for a test.

Yea I think I might try sand bags next and just see what it does? The thing about trim is this. That lip that runs across the back that you see in the pick ( not sure what its called?) splash bar?? is not dead even against the transom. there is a gap in there on both sides of about maybe a quarter of an inch. so when I get on plane and trim up water comes straight up the transom though this gap and over in to the back of my boat. so thats why I hardly ever used the trim. I will sometimes Idle with it up and that doesnt hurt anything. Bottom line is I need to run a bead of silicone on that gap to fill it in, just havent done it.

 

[fender66]

This tells me (since you aren't using the trim) that you should try using it to check for improvement. It's the easiest test to try. Then....work on sealing the gap.

 

[Darkside]

By all means, do everything else first, shifting weight ect… We’ve found that a balanced boat keeps the aft of the boat out of harm’s way during takeoff, but it does not improve the overall speed. Some get on plane quicker, some even lose a mile o two.

We’ve done a lot of tunnel work here in the east to save our intakes. I have personally designed 3 tunnels and the first was a complete disappointment. The chapter is certainly not written, but for 4-8 degree hulls we find the jet tunnels need to be 2”-3” deep. Length is not as critical but I’ve not had any luck with anything less than 22” and I’ve seen some that were 6’ long. Width is critical. I prefer 45 degree sides rather than 90 to enhance water flow from the sides in a turn. 90 degree sides creates a waterfall effect and increased cavitation for us here. Tunnel width should be just wide enough that as the intake turns hard left and right, it still has water flow. Too narrow a tunnel and you have issues. 17-18” wide (on the bottom) and 15” wide at the top works well.

Your pictures of the tunnel look real wide and deeper than what we use here. Doesn’t look as deep as a prop tunnel common on duck boats out here, but it is larger than we have and could cause your issues with chop and wind more than weight distribution. If the trim and weight stuff doesn’t fix the problem. Welding in a plate to decease tunnel height “or” closing the tunnel altogether is an option. Closing it in means dripping the engine accordingly.

Another fix we have used on production hulls is to put a transom wedge in to increase the trim angle (offer more range) depending on what is needed.

https://www.bobsmachine.com/Products/transom_wedges.cfm

Also, here are some examples of smaller jet tunnels.



Hope some of this helps. –Chris G.

 

[red450r]

How much gap is between the tunnel and the leading edge of the foot? maybe try pop riviting a piece of uhmw to close the gap.


such as https://www.tinboats.net/forum/viewtopic.php?f=48&t=19796

 

[Darkside]

We extend the tunnel (and trim tabs) and bolt the UHMW down tight against the top of the intake-shoe.



Picture above shows the tunnel lid. Also have some examples with non-custom tunnel crafts if you're interested. The lid just directs / forces the water into the tunnel vs. allowing it to blow past it. Really can make a difference.

 

[HoytHunter69]

First off guys thanks for the help. I just went and looked and the foot is dead even with the top of the tunnel. but that angle I was calling a splash pan? that runs left to right acroos my transom is about 2 1/2 inches over the foot. maybe I need to get that dropped right down on the foot like that pic of the UMHW? Also those two pieces that people put on each side of the foot? I heard they help direct water to the foot and help the boat bite in a turn? is this true? maybe that would help? Thanks again guys!

 

[HoytHunter69]

We extend the tunnel (and trim tabs) and bolt the UHMW down tight against the top of the intake-shoe.



Picture above shows the tunnel lid. Also have some examples with non-custom tunnel crafts if you're interested. The lid just directs / forces the water into the tunnel vs. allowing it to blow past it. Really can make a difference.

As I said I might need to lower mine to direct some of the water in the intake ? thanks for your help!

 

[fatherfire89]

As far as riding nose up, definitely check for water buildup in the flotation pods. I know some foams do absorb water--something about closed cell foam vs open cell foam or something like that.

I have a 1448 with a 50/35 and a 12 gallon tank up front. The battery is under the center console just behind the middle bench. I think it's only moving at about 90% of full speed with that much weight up front but it does stay very level on the water; floating or running full speed.

As far as water splashing goes, see the document below from outboardjets.com. I used this method for a 1/32" splash guard and don't have any splash up problems at all. But I can't say the no splashing is strictly due to the addition of that splash guard.

Feel free to ask questions... haha we love this stuff.

 

[HoytHunter69]

Thanks again! great info. I really want some of those fins to go on each side of my intake. I heard they really direct water in to the pump pretty well? good info!

 

[fatherfire89]

I haven't heard much about the effects of intake fins but I would imagine they help reduce cavitation to some degree. A lot of people in Alaska use them but I haven't seen a ton of them here in Montana.