Jet foot height question

[pauloosterheert]

I haven’t had a chance to run my new setup yet, but I’m wondering how you think it will run. I have a 25 Merc factory jet on a 1548 Tracker Grizzly mod v. The foot sits 7 inches behind the bottom hull edge. The leading edge of the shoe is 1.75 inches above the lowest point of the v. The bolt on the side of the the shoe is 1.25 inches above the lowest point of the v.

 

[Still Afloat]

I’m a beginner with jets but, it sounds like you’re in the ballpark. It will be interesting to hear what others with more experience say. Please keep us posted.

I also have a Merc 25 jet. Mine is on a Lowe 1448M that I’m rigging this winter. It’s too heavy to safely test on my boat without more weight up front or pods. In a squirrelly test with the front of the foot about an 1” above the flat hull it was doing about 22mph at WOT. It can probably do a little better with some fine tuning.

FYI - The same hull with a Suzuki F9.9/20hp conversion will do 27mph but, the Zuk is a prop and about 90 lbs lighter than the Merc jet.

 

[FuzzyGrub]

Welcome to TinBoats!

Can you post a pic of the side view? Are the measurements with the trim, all the way in/down? If the leading edge of the foot is 7" away from the transom, that seems a tad far.

We had a Tracker Grizzly 1448 mod-V. It was cockpit style and was a heavy boat. The 25 jet might be on the low side for your 1548. If a tiller, plan on moving weight forward. Batteries, gas, etc.

 

[pauloosterheert]

I’m a beginner with jets but, it sounds like you’re in the ballpark. It will be interesting to hear what others with more experience say. Please keep us posted.

I also have a Merc 25 jet. Mine is on a Lowe 1448M that I’m rigging this winter. It’s too heavy to safely test on my boat without more weight up front or pods. In a squirrelly test with the front of the foot about an 1” above the flat hull it was doing about 22mph at WOT. It can probably do a little better with some fine tuning.

FYI - The same hull with a Suzuki F9.9/20hp conversion will do 27mph but, the Zuk is a prop and about 90 lbs lighter than the Merc jet.

I appreciate the response and will keep you posted.

 

[pauloosterheert]

Welcome to TinBoats!

Can you post a pic of the side view? Are the measurements with the trim, all the way in/down? If the leading edge of the foot is 7" away from the transom, that seems a tad far.

We had a Tracker Grizzly 1448 mod-V. It was cockpit style and was a heavy boat. The 25 jet might be on the low side for your 1548. If a tiller, plan on moving weight forward. Batteries, gas, etc.

Side view is difficult with the pods. It is trimmed up 2nd from the top hole. I have a 7 degree angled transom, so trimming it in/down angles the jet downward and actually raises the leading edge of the foot more.

 

[FuzzyGrub]

Side view is difficult with the pods. It is trimmed up 2nd from the top hole. I have a 7 degree angled transom, so trimming it in/down angles the jet downward and actually raises the leading edge of the foot more.

OK, it sounds like you are in the middle trim position, which is usually perpendicular. Don't go further up/out, it won't get enough water. In its current position, I think it will take longer to get on plane, but will be likely to be the highest speed position.

There is no way to tell for sure. Every set-up is different. Just have to test it, and then try the further in trim positions. Might have to lower the motor some. Also, could try side plates if you get some cavitation with trim all the way in. Also, look into adding a splash plate.

The pods will help with the weight, but you will probably still need some redistribution.

PS: I re-read your trim position. 2nd hole from top. If this is a "standard" 5-position manual trim, you might be past the perpendicular position. If you haven't yet, allot of good set-up info on OutBoardJets. Read the FAQs, too.

 

[pauloosterheert]

OK, it sounds like you are in the middle trim position, which is usually perpendicular. Don't go further up/out, it won't get enough water. In its current position, I think it will take longer to get on plane, but will be likely to be the highest speed position.

There is no way to tell for sure. Every set-up is different. Just have to test it, and then try the further in trim positions. Might have to lower the motor some. Also, could try side plates if you get some cavitation with trim all the way in. Also, look into adding a splash plate.

The pods will help with the weight, but you will probably still need some redistribution.

PS: I re-read your trim position. 2nd hole from top. If this is a "standard" 5-position manual trim, you might be past the perpendicular position. If you haven't yet, allot of good set-up info on OutBoardJets. Read the FAQs, too.

Thank you. That photo looks to be very similar to the position I’m describing except without the plates. When you say perpendicular position, the shaft is perpendicular to the waterline but not perpendicular to the angled transom.

 

[FuzzyGrub]

Thank you. That photo looks to be very similar to the position I’m describing except without the plates. When you say perpendicular position, the shaft is perpendicular to the waterline but not perpendicular to the angled transom.

Yes, but technically they want the pump to shoot the water straight back. See 7B: Set-up

Note: the picture is a flat bottom hull with a tunnel, vs a mod-V.

 

[JL8Jeff]

The front of the foot should be even with the bottom of the boat or tunnel so the rear of the foot will be lower. There needs to be a bit of an angle from the front (higher) to the back (lower) or you will get some porpoising and probably some major sprayback that comes up over the transom. I run with my motor like this and if I tilt it up much at all, the spray gets bad and it will lift the bow. It will help if you can post some pictures but it took me 3-4 adjustments to find the best height. I kept going up until it sprayed really bad and went back down 1 hole. I also had to add the transom shims to get it tucked up as far as possible to keep the bow down and reduce the porposiing.

 

[pauloosterheert]

I finally got out on a test drive and was disappointed. I tried all different trim positions and barely got on plane. Motor accelerated nice at low speed and once it got just barely planed it would cavitate with high RPMs. I think the 1548 just isn’t a good match for a jet. I’m already at the max HP for the hull and would have to go up over 25hp for a longer shaft.

 

[FuzzyGrub]

Cavitating on plane, you are sucking air. Maybe something on the hull is causing turbulance? Can you drop the motor one position lower? I'd try that before giving up. If it performs better, than those side fins might allow you to raise it back up to where you had it.

 

[pauloosterheert]

Cavitating on plane, you are sucking air. Maybe something on the hull is causing turbulance? Can you drop the motor one position lower? I'd try that before giving up. If it performs better, than those side fins might allow you to raise it back up to where you had it.

I cannot drop any further. I’m as low as it goes. Tracker put a 23.5” transom on the 1548, so it’s kind of in between shaft lengths. I do appreciate your response.

 

[FuzzyGrub]

I'm not sure if the fins would fix your problem and they would be about a $100 expierment, Not sure if they make them for the "small" foot, that I assume your motor has, either.

 

[Still Afloat]

I wonder if a flap would help. These seem fairly common, at least for tunnel hulls. It’s basically a flap that extends from the transom over the top of the foot.

 

[FuzzyGrub]

When we first got the jet and going thru the break-in procedure, tried to slowly get on plane, as break-in procedure specified. It would cavitate at a certain point. Called the dealer, and they told us to "gas it" over the hump. Just give it full trottle from launch. No problem since then. Just mentioning it, in case you were doing the same.

 

[JL8Jeff]

You may want to try the transom wedges to tuck the foot in a little closer. I have them on my boat because it would porpoise badly without them but they help get the foot tucked in as well. The foot being 7" behind the transom sounds too far back,, mine is around 3-3.5" but I also have the jet tunnel and 2" extension.

https://www.amazon.com/T-H-Degre-Po...lpcontext&ref_=fplfs&psc=1&smid=ATVPDKIKX0DER