Motor mounting height

[JustDave]

I own a 2014 Maverick Hpx 17-V with an F70. I have always thought the motor was mounted too low and it seemed I was always making contact with bottom when running shallow. I went ahead a couple weeks ago and raised the motor to the next mounting hole, about an inch,  after hitting a rock and doing some nice skeg and prop damage. So far I think the minor adjustment has boosted performance as well as confidence. I haven't blown out on hard turns and the hole shot and responsiveness seems to be better. Has anyone else experimented with different motor heights on the hpx 17? I know the general rules for the cavitation plate lining up with keel etc but I think the pocket on the back of the hull allows for more leeway in mounting height. Id be interested in hearing other opinions and I may even go higher and see what happens.

[hawg]

I'm running mine as low as it can go. Two friends with the same boat are running it all the way down as well. I'd like to raise it a notch to see if it performs any better. Can you tell me what prop you're running on the F70?

[Coto]

I have a 115 and it's mounted on the second to the top hole on the engine and there are no issues at all, it performs as expected. I don't know what experience you have in boat so I'm just going to ask, are you trimming the motor up once you are on plane or still leaving it all the way down? I had a friend who owned a boat for a while and did not know about trimming a motor. While running I pushed the button for him and and the astonishment on his face looked like he discovered gold. 

[hawg]

Coto,

On my 17 HPXV, I can only trim the motor (F70) up one or two ticks on the Yamaha trim gauge before the bow starts to porpoise. Using trim tabs to hold the bow down degrades the performance enough that it is not a viable option. The prop will begin to blow out at about 3 ticks up. Overall, the boat's performance is good, but I'm interested if it would improve slightly (hole shot and top end speed) with the engine raised a notch. 

 

[Coto]

Gotcha, shouldn’t be a problem to play around with it. Rent yourself a hydraulic engine lift and try it out. Let us know how it goes I would be interested in knowing since that 70 will be my choice for a repower God forbid my 115 goes kaput.

[hawg]

I've got a stout oak tree in my back yard that doubles as an engine lift. I'll let you know what I find out. Given the current mob scene at the local (MIami) marinas, it might be a while.

[geeviam]

On 5/8/2020 at 7:05 PM, JustDave said:

I own a 2014 Maverick Hpx 17-V with an F70. I have always thought the motor was mounted too low and it seemed I was always making contact with bottom when running shallow. I went ahead a couple weeks ago and raised the motor to the next mounting hole, about an inch,  after hitting a rock and doing some nice skeg and prop damage. So far I think the minor adjustment has boosted performance as well as confidence. I haven't blown out on hard turns and the hole shot and responsiveness seems to be better. Has anyone else experimented with different motor heights on the hpx 17? I know the general rules for the cavitation plate lining up with keel etc but I think the pocket on the back of the hull allows for more leeway in mounting height. Id be interested in hearing other opinions and I may even go higher and see what happens.

The rule of thumb that I was taught long ago was bottom of AV plate (with boat hull keel and motor AV plate leveled) should be in line with the aft-bottom of the keel, on a straight/flat transom with no setback pocket.  For every 11 inches of setback (pocket depth - bow to stern direction), move the AV plate up 1 inch.  Your motor mount bolt holes may be off of this mark a little, but it's a good starting point.

[geeviam]

On 5/15/2020 at 10:18 AM, hawg said:

Coto,

On my 17 HPXV, I can only trim the motor (F70) up one or two ticks on the Yamaha trim gauge before the bow starts to porpoise. Using trim tabs to hold the bow down degrades the performance enough that it is not a viable option. The prop will begin to blow out at about 3 ticks up. Overall, the boat's performance is good, but I'm interested if it would improve slightly (hole shot and top end speed) with the engine raised a notch. 

 

Which model and size prop are you running, with this problem?

[Coto]

Don’t forget the fresh water ramps for canals. I prop test my boats at Markham Park which is by the Everglades. I’m sure you can use the snapper creek ramp or something like that to avoid The crazy at black point or Matheson hammock.

[hawg]

It's a 2001 17 HPXV with a 2013 Yamaha F70 running a PowerTech NRS3R14PYM90 prop. I don't consider it a problem, I just want to be sure I'm getting the best possible performance from this combination.

[geeviam]

16 hours ago, hawg said:

It's a 2001 17 HPXV with a 2013 Yamaha F70 running a PowerTech NRS3R14PYM90 prop. I don't consider it a problem, I just want to be sure I'm getting the best possible performance from this combination.

My advice is first see if Powertech has a better prop solution for you.  This isn't the first I've heard of porpoising issues with a NRS.  Another possibility would be to talk with Jack Foreman at Crossroad Propeller in Port Lavaca, Texas.  He makes custom cupped props for shallow running skiffs in your horsepower range.

[geeviam]

On 5/17/2020 at 8:26 AM, hawg said:

It's a 2001 17 HPXV with a 2013 Yamaha F70 running a PowerTech NRS3R14PYM90 prop. I don't consider it a problem, I just want to be sure I'm getting the best possible performance from this combination.

I realize your question was more about motor height and not about props, but since you mentioned you are already experiencing porpoising and blowout when trimming up, I thought I'd suggest a prop change rather than raising the motor height.  Blowout usually means the motor height is already too high for the prop you are using.  And, a prop that loses grip can contribute to a porpoising problem because it is not consistently hooked up enough to lift and hold the bow steady.

[Bruce J]

21 hours ago, geeviam said:

My advice is first see if Powertech has a better prop solution for you.  This isn't the first I've heard of porpoising issues with a NRS.  Another possibility would be to talk with Jack Foreman at Crossroad Propeller in Port Lavaca, Texas.  He makes custom cupped props for shallow running skiffs in your horsepower range.

I have one of Jack’s props on my HPXT with an F70 motor.  It grabs well in the highest mounting position and then at the top of Jack-plate range.  I couldn’t blow the thing out.  But the T is quite a different hull than the V, and Jack’s props are really geared for super shallow boats, usually with tunnels.  He might makes some others, but there are very few HPXV’s in Texas, so maybe not. 

[hawg]

Moved the engine up one hole. I don't notice a huge difference in performance. Top RPM up 150 turns. Top end up one knot. Nose still porpoises when the engine is up more that a click or two.

[geeviam]

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[geeviam]

On 5/18/2020 at 11:13 PM, Bruce J said:

I have one of Jack’s props on my HPXT with an F70 motor.  It grabs well in the highest mounting position and then at the top of Jack-plate range.  I couldn’t blow the thing out.  But the T is quite a different hull than the V, and Jack’s props are really geared for super shallow boats, usually with tunnels.  He might makes some others, but there are very few HPXV’s in Texas, so maybe not. 

Not mine, but here is a used Jack Foreman prop for sale, that came off a F70.  Looks like some serious tip cup.  I'll bet a prop like this, with such good grip, and the ability to stay hooked up when running the motor super high on the transom, would be a good anti-porpoising prop on a non-tunnel hull too, as long as it doesn't generate excessive steering torque.

https://www.microskiff.com/threads/jack-foreman-prop.80804/

[Bruce J]

That’s a really big port they’ve drilled in that Foreman prop. I would pay the extra bucks to get an unmodified one from Jack.