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Motor Height / Cavitation Plates

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leftyonly

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We have a new to us 2013 model 2375GCW with Express Package and strakes on both sides of all three toons.  Power is a Mercury 150 4S.


Only been out in it a few times so far, but noticed that it tends to very easily cavitate/ventilate when turning at moderate speed on plane (22-26 mph) and trimmed out to level.  We can trim it in when turning and it's not too bad, but then hulls/strakes digs in and give some adverse roll.  Also noted that under some circumstances, there is a lot of water thrown up around the motor on plane.


Question is how to evaluate whether the motor is rigged to the proper height for this setup?  Is there a formula or instructions for setting proper height?


Also, are add-on cavitation plates useful on pontoon motors to reduce prop ventilation issues?


The prop/motor setup seems to be good.  It has a top speed of approximately 36 mph at 5600 rpm or so with 4 person load.  Looking to pull around some tubes and kneeboarders this summer and not sure if we will be able to maneuver for turnarounds without cavitation/ventilation.


Here are a couple of vids taken from another boat...


Bennington 2375GCW Express Cruise speed


Bennington 2375GCW Espress WOT
 
At that speed you need to trim down while making a turn.  Trim back up once completed.  Speed is only a factor.  The turning radius it what really makes the difference.  The sharper you turn at a faster speed, the more down trim required. 
 
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Trim down and you'll be good.
 
The outside strakes, as mentioned by the OP will dig in and cause the "adverse handling" he describes. So simply trimming in is too simple of an answer.


The Express tube is a compromise. All that water coming off the Express tube is "split" by the motor pod creating the water churning at the stern.


Not sure that engine height changes make much difference.


Propping may affect the cavitation, however without creating the "adverse effects."
 
Adding to my comments: The SPS doesn't have strakes on the outside of the outer tubes because the SPS "banks" (leans) into turns. A strake on the outside of the lowest tube (inside) could catch and cause "adverse handling," actually just less predictable outcome.


The express tube doesn't lean as much as the SPS in a turn, but as the OP writes, can still "catch a strake" during a turn.


An elliptical tube boat (2 tube) also does not bank into turns, but that's a discussion for a different thread.


Also, to elaborate on my comment about "engine height not making much of a difference, I did raise my motor one hole (to the top setting) and didn't realize any improvement in performance.


OP, have you tinkered with props? I went from a 13 pitch to a 15 pitch with good results. No cavitation or blowout. No problem on turns, but I also did not have those pesky strakes to deal with.
 
Thanks for the info.


The prop is a PowerTech OFS4R14PCL200 (4 Blade, 14 Pitch).  Don't have ready access to other props to test at this time, but will keep it in mind as we see how the boat performs over the summer watersports season.


Even if they are not the solution to the topic at hand, what the consensus on add-on cavitation plates?  Any use on pontoons?


 - Richard
 
Everything I've read about them directs towards smaller motors than a 150. Combatting this with trim is what I have always done.
 
leftyonly said:
Thanks for the info.


The prop is a PowerTech OFS4R14PCL200 (4 Blade, 14 Pitch).  Don't have ready access to other props to test at this time, but will keep it in mind as we see how the boat performs over the summer watersports season.


Even if they are not the solution to the topic at hand, what the consensus on add-on cavitation plates?  Any use on pontoons?


 - Richard
Click to expand...

Richard: The only time I have seen these plates (or wings) is on v-bottom boats that are underpowered. These devices probably assist in getting (or holding) the boat on plane. This isn't a factor for pontoon boats. In fact, I've never even seen one on a pontoon boat.


In my experience, a prop that gives great top speed (and yours is one of the better performing express tube boats I've heard of, top speed wise) is NOT necessarily the best when it comes to acceleration and related cavitation. Do experiment when the opportunity arises. The solution may be there in a different prop. 
 
I can't believe you are doing that kind of speed with the top 


I would think the top would create drag and be a problem on its own


I never use top with any speed, to me it is for sitting on the lake and keeping the sun from baking me  (lol)


Awesome Boat 


Pittsburgh-Bicentennial-Feature.jpg
 
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Won't be running at any speed other than a leisurely cruise with the top up any more.  In hindsight, it was probably a mistake to do so on that day. It did not seem to cause or suffer any ill effects.


Excited about the new boat I suppose.


FWIW, we will probably not be doing any more running side-by-side like that anymore either.  Too much distraction for both operators with the boats in close proximity at speed and the potential to encounter other boat traffic.  It was fun though... B)
 
Randy,


Thanks for the info.  I have seen the add-on caviation plates like these on tunnel hull/shallow water boats where the jack plates allow the prop shaft to actually be above the waterline.  Not exactly the same as the whale tails since they are not intended to provide lift, but function only to keep water on the prop.  Image below....


KPPlate.jpg
 
I've never seen such a contraption before. Thanks for the introduction.
 
One example that has good reviews/following with the shallow water/tunnel hull...


http://stiffypushpoles.com/shawwing-cavitation-plates


I have no affiliation or experience with them, providing the link for reference. (Mods please kill link if it is improper to post...)


Hoping someone had experience with something like this on a pontoon and could enlighten us.
 
leftyonly said:
Won't be running at any speed other than a leisurely cruise with the top up any more.  In hindsight, it was probably a mistake to do so on that day. It did not seem to cause or suffer any ill effects.
Click to expand...

I've run with both single bimini and double bimini at high speeds without any problem (I won't say exactly what speed or I might void the warranty  :)  ).  


I test drove other boats with poor bimini frames and they rattled a LOT.  I love the quality build of the Bennington, and the bimini frame is very solid.  Don't get sunburned on a decent speed cruise for fear of hurting the frame.  
 
JTaylor said:
I've run with both single bimini and double bimini at high speeds without any problem (I won't say exactly what speed or I might void the warranty  :)  ).  


I test drove other boats with poor bimini frames and they rattled a LOT.  I love the quality build of the Bennington, and the bimini frame is very solid.  Don't get sunburned on a decent speed cruise for fear of hurting the frame.  
Click to expand...

Good to know.  Thanks!
 
This is just something I have come across surfing the interwebs:


http://www.stingrayhydrofoils.com/stingray-classic/


Suppose to assist in a few areas and are designed for v-hull boats and pontoon applications.  Just throwing this out there.


I have never used one and have never seen one used either. 
 
leftyonly said:
One example that has good reviews/following with the shallow water/tunnel hull...


http://stiffypushpoles.com/shawwing-cavitation-plates


I have no affiliation or experience with them, providing the link for reference. (Mods please kill link if it is improper to post...)


Hoping someone had experience with something like this on a pontoon and could enlighten us.
Click to expand...

I just skimmed their site briefly and saw no mention of pontoon boats at all.
 
JaccFrost said:
This is just something I have come across surfing the interwebs:


http://www.stingrayhydrofoils.com/stingray-classic/


Suppose to assist in a few areas and are designed for v-hull boats and pontoon applications.  Just throwing this out there.


I have never used one and have never seen one used either. 
Click to expand...

Those worked great on my bowrider.  A lot of people on my lake have them.  I bought one for my Tritoon but have not put it on yet.
 
leftyonly said:
We have a new to us 2013 model 2375GCW with Express Package and strakes on both sides of all three toons.  Power is a Mercury 150 4S.


Only been out in it a few times so far, but noticed that it tends to very easily cavitate/ventilate when turning at moderate speed on plane (22-26 mph) and trimmed out to level.  We can trim it in when turning and it's not too bad, but then hulls/strakes digs in and give some adverse roll.  Also noted that under some circumstances, there is a lot of water thrown up around the motor on plane.


Question is how to evaluate whether the motor is rigged to the proper height for this setup?  Is there a formula or instructions for setting proper height?


Also, are add-on cavitation plates useful on pontoon motors to reduce prop ventilation issues?


The prop/motor setup seems to be good.  It has a top speed of approximately 36 mph at 5600 rpm or so with 4 person load.  Looking to pull around some tubes and kneeboarders this summer and not sure if we will be able to maneuver for turnarounds without cavitation/ventilation.


Here are a couple of vids taken from another boat...


Bennington 2375GCW Express Cruise speed


Bennington 2375GCW Espress WOT
Click to expand...

I have the same setup on our S (150 4S with Express and 6 strakes) and had the same ventilation issue.  For me, it was the prop.


I have two props.  First is a 15 pitch Black Max.  It ventilated just like you describe.  The motor had to be trimmed ALL the way down before it wouldn't ventilate in a tight turn.  With even just the slightest amount of trim, it would ventilate.


Then I got a 15 pitch Enertia (Thanks Todd!).  It made a world of difference.  I get a LOT more trim range before it ventilates in a turn.  I can press the trim up button for about 3 seconds now, and it still won't ventilate.  The other prop ventilated with just a quick tap on the up-trim button.


So, that's one possible solution for you.  Nice videos by the way!  That second one got a little close to the edge for me, but maybe it was the zoom.  Good luck!
 
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