Sudolicious Posted December 7, 2019 Report Share Posted December 7, 2019 So before you say it, I spoke with Marcus, two times. Great guy. Even he is stumped cause he has never seen a 2002 17' HPXV with a jack plate and that might be the issue so I thought I would see what you guys thought. I installed a jack plate, just a lift so it does not push the motor back too far, maybe a couple inches. I am having a really hard time with cavitation. Simutaneously I put a 4 blade prop on there with some stern lift. RXBR15PYM90 It cavitates constantly. Hard to find a sweet spot.WOT is 34.8 at maybe 50 RPMS if trimmed up. Cant get RPMs any higher than that. I had the engine rebuilt, 90 Yamadog, has some weight on it, me and pretty heavy poling platform, trolling motor and casting platform. So my question is does anyone run or know of a boat like this with a jacklate and can that be the cause of the constant cavitation. Should I go back to the 3 blade? Should I get a prop with less stern lift, it seems like the splash line is pretty far forwardin front of my feet. Would like to hear if anyone has any experience? Quote Link to comment Share on other sites More sharing options...
geeviam Posted December 7, 2019 Report Share Posted December 7, 2019 1 hour ago, Sudolicious said: I installed a jack plate, just a lift so it does not push the motor back too far, maybe a couple inches. I am having a really hard time with cavitation. Simutaneously I put a 4 blade prop on there with some stern lift. RXBR15PYM90 Which make, model, size jack plate? Reason I ask is: adding a JP adds about 1.5" to 2" of built-in motor height on the transom. Without more setback to compensate for that extra lift, your prop is probably too high on the surface of the water, and losing bite due to ventilation. Side note: I'd like to see more boat manufacturers and outboard installers change old habits... Once they know the optimum height to install the outboard on the transom of a particular model boat, they should drill the mounting holes in the transom 1.5" lower (or 2 motor mount holes lower, center to center). Then the motor can be mounted at just the right height in the third hole from the top, if no jack plate is used. If a jack plate is used, it could be installed in the top hole (as low as possible), with motor mounted at the top hole as well. The cavitation problems associated with adding jack plates with short setback (4" and 6") would be eliminated and the operator would have use of the full range of jack plate lift adjustment. Edit: The only risk associated with mounting a JP this way is: the operator would have to be careful when tilting the outboard with the jack plate all the way down, and make sure the outboard steering components have enough clearance above the top of the transom. The JP would have to be raised a bit before tilting the outboard up high - always. Quote Link to comment Share on other sites More sharing options...
ToddM Posted June 25, 2020 Report Share Posted June 25, 2020 On 12/7/2019 at 9:18 AM, Sudolicious said: So before you say it, I spoke with Marcus, two times. Great guy. Even he is stumped cause he has never seen a 2002 17' HPXV with a jack plate and that might be the issue so I thought I would see what you guys thought. I installed a jack plate, just a lift so it does not push the motor back too far, maybe a couple inches. I am having a really hard time with cavitation. Simutaneously I put a 4 blade prop on there with some stern lift. RXBR15PYM90 It cavitates constantly. Hard to find a sweet spot.WOT is 34.8 at maybe 50 RPMS if trimmed up. Cant get RPMs any higher than that. I had the engine rebuilt, 90 Yamadog, has some weight on it, me and pretty heavy poling platform, trolling motor and casting platform. So my question is does anyone run or know of a boat like this with a jacklate and can that be the cause of the constant cavitation. Should I go back to the 3 blade? Should I get a prop with less stern lift, it seems like the splash line is pretty far forwardin front of my feet. Would like to hear if anyone has any experience? Following along. Did you find a resolution? Putting a jack plate on a HPX 17 V with 2stroke 115 Yamaha. Quote Link to comment Share on other sites More sharing options...
lurem Posted June 25, 2020 Report Share Posted June 25, 2020 Geeviam, Instead of having boat manufacturers drill different holes how about the jackplate companies design the mounting holes lower so you have a level base starting point of where the engine was originally mounted and then adjust for your situation as needed? 1 Quote Link to comment Share on other sites More sharing options...
geeviam Posted June 25, 2020 Report Share Posted June 25, 2020 20 minutes ago, lurem said: Geeviam, Instead of having boat manufacturers drill different holes how about the jackplate companies design the mounting holes lower so you have a level base starting point of where the engine was originally mounted and then adjust for your situation as needed? Sounds good Dale. I'm all for it! Quote Link to comment Share on other sites More sharing options...
Sudolicious Posted January 19, 2021 Author Report Share Posted January 19, 2021 I can update that I have not found a resolution to this issue and been using the boat a lot and need to do something soon. The solution may be to remove the jack plate, I don't think there is enough clearing for the steering components as mentioned above to lower the engine any further.. I think the little bit of setback from the jack plate just causes the prop to spin in soft or aerated water. Question if you are following this thread, if I re-powered with the heavier 4 Stroke 90, would that potentially solve this issue?? Quote Link to comment Share on other sites More sharing options...
whichwaysup Posted January 19, 2021 Report Share Posted January 19, 2021 Okay, so, I'm sure you thought of this, but since I didn't see it in your update, I'll post it. It sounds like you've changed two variables: Prop and Jack plate. Now you have an issue. The first logical thing to do is to remove one of the variables and see what happens. Have you swapped back to the 3 blade? A prop swap is a 20 minute job. If you still have cavitation, you know its the jack plate, which is the harder thing to change out but now you know what the cause is. Remove jack plate, put the 4 blade on and see what you end up with. Again, I'm sure you've thought of this, so no offense intended if I'm stating the obvious. Quote Link to comment Share on other sites More sharing options...
Sudolicious Posted January 28, 2021 Author Report Share Posted January 28, 2021 Yes I am back to the 3 blade, no change in the cavitation. I have a call into the manufacturer of the Jack Plate, Bobs Marine Shop, I saw something in one of the posts that made sense that there is not enough set back. I will ask a specialist and repost. Quote Link to comment Share on other sites More sharing options...
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