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Dunphy X-55 fine tuning

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    Posted: July-11-2019 at 1:14pm
Hi folks,

I noticed there is are some Dunphy X-55 owners on this site, more than anywhere else, so I'm hoping I can get some info about this boat I've had for a couple years.

I am currently getting about 43 mph top speed with a bit of porpoising, what feels like a plowing porpoise rather than a bow up porpoise. My quest is to get it up to the 50-55mph advertised top speed.

It was restored about 15 years ago, and while is mostly stock running gear, it's hard to know what is, and is not original.

Here are the specs.
Prop 12 x 13 not original. Original prop was a Dyna Jet 12x15 cupped. Currently sourcing a new prop. Sent a request to michigan wheel. Thinking about the DJX 12x16 cupped.

Drive angle 16 degrees. Strut part number is D-160 cast into the strut, so guessing this is original, but who knows.

Engine appears to be in the original location based off the engine mounts. There is room to mount the engine lower, So with a new strut the drive angle could be reduced. There is only 1.5" of prop to hull clearance already at this steep angle, so that makes me think 16 degrees is original.

Other issue I have is poor maneuvering control at idle. Rudder turns to an angle of just shy of 40 degrees either direction. I can move the cable to the inner hole on the rudder shaft and get probably 5 more degrees out of it. But the rudder seems maybe a bit small, and doesn't extend down as far as I would think it should. It also extends beyond the transom and so kicks up a bit of a spray during high speed turns and will even ventilate and lose some control in sharper high speed turns. Rudder has 2600-26D stamped into it.

Thank you for any input, and I'll keep you posted on how things go fine tuning this boat.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-11-2019 at 2:18pm
Hi Jon

Very soon you will meet your new best friend Pete.

I'm sure he'll have some input for you

In the meantime you can click on the link below and see what's on CCF dealing with x-55's

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-11-2019 at 3:12pm
Thanks for the reply. My boat is far from original, but it does have the YH carbs and original trailer, so that's a plus. I have the original wheels and tires for the trailer as well, but they aren't made for Texas highway travel speeds.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-11-2019 at 8:12pm
Jon,
What RPM is the 312 turning up? Unless the 12x13 has been re pitched, the 13 will over rev the engine. The original 12x15 will crank the engine up to about 4300 - 4400 and that's what you should be at. One note regarding the original 12x15 Michigan's is they were modified by grinding a concave relief in the hub. I still run the original and there is a noticeable difference from the stock 12x15 Michigan.

Stick with the original geometry with engine/shaft angle as it's one of the contributing factors that got the hull patent and the clamed 55 MPH speed. Mine's been radar clocked (before GPS) at 54. The only one I know of that exceeded the 55 was our old ski club X. It came from the factory without any upholstery with the exception of the drivers seat. Don't expect 55 from yours with all the extra weight of the customization.

Poor maneuvering at idle? You're driving an inboard!!   

Do you know the history of the boat?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-11-2019 at 10:52pm
Thanks for the reply Pete. I appreciate your input. Boat started in WA and moved to ID where I got it. There are 50 hours on the meter which appears to have been added during the resto. I found it around 2013.   My guess is resto around early 2000’s.

Regarding the RPM. Somewhere between 3000 and 4500 at WOT. I love old gauges. Except for temp which is way too accurate usually on most old stuff, and will drive you crazy. I’ll take an idiot gauge for temp any day.

I’m installing a new tach where an aftermarket pitot tube Speedo is currently. I use my phone for speed.

I’m having fun seeing what this beauty will do. I’ve driven plenty of inboards small to large, and this is definitely the worst. I’m more confident maneuvering a 50’ sailboat than this.

Based on the restoration, which is top notch wood work but lacking mechanically, I question any of the geometry of the work. Not that I’ve found anything terribly out of sorts, but a few things have made me want to start from scratch rather than analyzing top down. It’s a lovely machine, and quite the hotrod of a ski boat. I look forward to perfecting it.

If someone wouldn’t mind checking the casting numbers on their strut and rudder, I would be ever so appreciative.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 6:00am
Originally posted by Extratx Extratx wrote:


I’m having fun seeing what this beauty will do. I’ve driven plenty of inboards small to large, and this is definitely the worst. I’m more confident maneuvering a 50’ sailboat than this.


Well there always has to be a best and a worst I suppose when you're comparing things.

In your case what makes it the "definitely the worst" ?

That's quite an RPM range at full throttle. Is that saying the tach is wacko and not accurate at all or you just haven't really noticed the RPM's at full throttle?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 6:03am
Originally posted by 8122pbrainard 8122pbrainard wrote:

Jon,
One note regarding the original 12x15 Michigan's is they were modified by grinding a concave relief in the hub. I still run the original and there is a noticeable difference from the stock 12x15 Michigan.


A picture is worth a thousand words right here Pete
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 7:24am
Originally posted by Extratx Extratx wrote:

My boat is far from original,<snip>


uh oh

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 7:41am
It’s like the rudder isn’t in the prop wash at all. There is no scooting the rear of the boat left and right. Basically requires a few + mph to start turning. The tightest 180 I could manage to pull was about 20-30 ft radius with lots of fwd and reverse. Pretty much the same radius as if I go full rudder and idle it.

Regarding the tach, it’s very bouncy. Should just say fast and slow, as that’s how accurate it is.

I too want to see a picture of this prop!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 7:59am
Originally posted by Extratx Extratx wrote:

It’s like the rudder isn’t in the prop wash at all. There is no scooting the rear of the boat left and right. Basically requires a few + mph to start turning. The tightest 180 I could manage to pull was about 20-30 ft radius with lots of fwd and reverse. Pretty much the same radius as if I go full rudder and idle it.

I too want to see a picture of this prop!

Originally posted by 8122pbrainard 8122pbrainard wrote:

Jon,
Poor maneuvering at idle? You're driving an inboard!!   

I'll work on getting the picture


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 8:54am
I'll get down to the boathouse later today and see if I can get a better picture that shows the modification but the concave ground out area is on the hub forward and into the blade just below my thumb. My understanding is Dunphy had a local prop shop in Oshkosh Wi. modify their props. The area ground out is were under some conditions there's cavitation that the modification eliminates. I have seen evidence of it on a couple props where the hub is eroded in the area.



With the stock 12x15 Michigan, speed and RPM (by a couple hundred) is reduced. When I first noticed the reduced performance, I took both props to a prop shop thinking there was a slight difference in pitch between the two but, both matched up with the 15" pitch block. He was the person who told me Dunphy had their prop shop do the modification. Asking him if he would grind out the area, he said no feeling the grind would reduce the strength. The unmodified prop went on one year and it ended up throwing one of it's blades. Concerned with the modified prop doing the same, I had it X-rayed. Not knowing what a good or bad prop should look like, I sent the Xray to Michigan Wheel. Then I called and talked with Michigan's chief engineer asking him what he thought. His response was he didn't know because he had never seen an Xray of one of his props before!!!!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 9:46am
Does this picture without the thumb show anything?

It's from the same prop installation thread as your other picture

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 9:56am
Ken,
The ground out area is behind the Photobucket banner.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 10:58am
Here are some pictures of my current setup. Would love to know if my strut and rudder are original or replacement.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 11:44am
Pete's probably out swimming with his phone to get a picture of his prop but if you click on the link, you'll find some pictures of his strut   

link
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 1:22pm
Your funny , Pete with a phone with a camera. He’s out trying to find film for his Polorid
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 1:44pm
I've taken some pics and will post here. Your rudder may not be OEM. Where your measured 8.25" deep, original is 9.0", and your width of 5.75" s/b closer to 6.5".
Confirming the 16 degree strut angle. ( D 160)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 1:46pm
here are the 'notches' in the stock 12x15 prop...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 1:49pm
Originally posted by Gary S Gary S wrote:

Your funny , Pete with a phone with a camera. He’s out trying to find film for his Polorid


That is funny.
I pictured him swimming with a pencil and some tracing paper...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 1:53pm
Ken,
Gary is correct, my phone doesn't take pictures! BTW, no swimming was needed.

Jon,
A PO of you X must have thought he was a marine architect because your drive train sure isn't original. I measured as close as I could and I got between 10 and 12 degrees on the angle but, the keel is angled back there too making it hard to be exact. Note that the strut and rudder is different. Also with a 12" prop, there's only about 3/4" clearance to the hull.





Here's a better picture showing the prop where it's been ground out. I was wrong, the modification is on the aft end of the hub and blade. The area is were the shadow is.



You mentioned the nose being planted. That would be the result with your steeper angle of the prop and shaft. All I can say is be REAL careful driving at higher speeds. With a nose planting, hulls can do a quick and unexpected 360 and even flipping. How's your liability insurance?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 2:34pm
Thanks for the photos guys! Definitely looks like my running gear is not original. Did you see any stamping on your strut?

Nose isn't planting so much as it's not hovering at speed. Feels that the porpoising is more from the water pushing the nose up, rather than nose too high and gravity pulling it back down. On an I/O it would be more like too much down trim rather than too much up trim. Definitely not to the point of danger, or digging in. No speed loss when it comes down. Just an annoyance.

I am going to track down my angle finder and measure the pictures. Should give an idea of the original shaft angle. Tonight I will photograph my engine mounts and maybe we can compare that as well.

Regarding the rudder, that explains alot! Mine is too small.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 2:37pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

Ken,
Also with a 12" prop, there's only about 3/4" clearance to the hull.


I have 1-1/2" of hull clearance with this 12" prop. I've read that a cupped prop will help lift the nose, so maybe 12x15 or 12x16 with a heavy cup will be what I need to avoid a complete driveline refit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Extratx Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 2:40pm
Also, I noticed the stock rudder has a good bit of surface in front of the shaft, where I have very little, which is definitely affecting my low speed maneuvering, as it isn't catching enough prop wash.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 3:14pm
Jon,
What was done to the hull? Has it been fiber glassed?

The downfall of the X55 was their bottoms. They had purchassed a large quantity of Mahogany from the Phillipines. Unknown to them was the veneer used had a dormate fungas in it and when it got damp the rot began plus delamination. Dunphy replaced at there own expence lots of bottoms the first couple of years. Mine was not one of them they replaced so I ended up replacing the bottom ply back and inner and outer keels around 76.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 4:43pm
Originally posted by Extratx Extratx wrote:

Thanks for the photos guys! Definitely looks like my running gear is not original. Did you see any stamping on your strut?   


Yes, barely legible "D 160" on port side.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 4:51pm
Extratx, how about a couple photos of the motor mounts/mounting for comparison...?

One of the characteristics of the X55 is it's level-riding hull at speed.
See attached video:
https://www.youtube.com/watch?v=QalrPT0h9-k
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 4:54pm
Jon,
Taking another look at my strut angle, I'd say Brian's 16 degree measurement is correct. Go by his and not the angle I came up with.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 5:37pm
Originally posted by MourningWood MourningWood wrote:

Extratx, how about a couple photos of the motor mounts/mounting for comparison...?

One of the characteristics of the X55 is it's level-riding hull at speed.
See attached video:
https://www.youtube.com/watch?v=QalrPT0h9-k


Here's a direct link


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Faceplant Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 9:18pm
Wow !! Didn't know that they were that fast .
I used to hang ten - now I hang six . And another thing - "GET OFF MY LAWN.".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: July-12-2019 at 9:37pm
I have told this to Pete years ago when we were discussing his at Green Lake the year he brought it down. There was one on my chain back in roughly 67-69,and I believe he knows of it with later owners. Anyway these local "hooligans" used to beat on it constantly not going fast but making it porpoise. Probably wore out the cable working the throttle.... dont ever remember them skiing behind it
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