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TomW1
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Re: Extreme Flats 20 Problems

Post by TomW1 »

The one problem he has with keeping the 40HP Merc is that he is limited to a 10-11" inch prop. Here is a good one from Power Tech he might want to start to start with http://www.ptprop.com/index.php?page=sh ... &Itemid=46 It has high rake, 20%, and good cup. PT might be able to work with him if the cup is not enough.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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wegcagle
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Re: Extreme Flats 20 Problems

Post by wegcagle »

Dan,

I'll start this off by saying that I am by NO means the most experienced person in this discussion. I can count the number of tunnel hulls I've ridden in on one hand. That being said....it seems like a small tunnel extension (like the picture below) would keep the water from coming out of the tunnel and up the space in your jackplate. As long as it's not too long (and blocks you from trimming the jackplate up and down).

Can anybody think of a reason this wouldn't solve the problem?

Image

Will
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cali123
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Re: Extreme Flats 20 Problems

Post by cali123 »

A tunnel extension is a great idea but first the motor has to be mounted in the right position. It looks to me that the motor/jackplate is mounted 4 inches too low. Once proper position is accomplished, the problem will go away.

TomW1
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Re: Extreme Flats 20 Problems

Post by TomW1 »

cali123 wrote:A tunnel extension is a great idea but first the motor has to be mounted in the right position. It looks to me that the motor/jackplate is mounted 4 inches too low. Once proper position is accomplished, the problem will go away.
Agreed and until you get some type of tachometer to measure engine rpms and engine performance.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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stickystuff
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Re: Extreme Flats 20 Problems

Post by stickystuff »

A little late on this. You def. need to have 20"" from top of tunnel to top,of transom.Mount J Plate flush with top of transom.Boat was originally designed as a stripped don model to keep it extremely light.Very first one built had a 25 HP. It ran extremely shallow but did not have a lot of speed. I saw it run in Jacksonville at our first boat rendezvous. speed was approx 15 to 20 mph. since then when Jacqu.es and I talked every one wanted to add Sole,s bigger engines etc.I have pictures of the first hull built and running.Beautiful boat. all open design as built. will have to dig them up and try to post or will send pics to Bateau.
Capt. Ken Owens

A little saw dust, a little glue, and a lot of love, and she will float.

CaptDan
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Re: Extreme Flats 20 Problems

Post by CaptDan »

OK Gang, Thanks for all your support. Just as a reminder, The transom on PLOVER is as designed 20" with the camber.
I was able to move the Jack Plate up one hole and the Motor Down 3 holes. The net effect raised the Motor 4 inches .
I have a 5" Jack Plate.

As suggested I just ran the boat solo with a temporary Tachometer. The results are WOT 3,100 RPM's with a 4 blade Aluminum, 10.5 x 13 prop. This = 21.4 MPH on the GPS. According to the owner's manual a 2015 40 HP Mercury 4-stroke WOT should = 5,500 - 6,000 RPM's Thanks for taking the time to help.

TomW1
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Re: Extreme Flats 20 Problems

Post by TomW1 »

Hi Capt. Now that you have everything pretty well set, I assume no more water coming in, and you can raise the motor into the wave coming out of the turnnel. Lets try to get you the right propeller. The one you have is obviously causing the engine to bog down. You need a prop that will let the motor revs reach the 5500 rpm range.

I would like to start with the way Cracker Larry and I propped his GF18. e-mail me at "deleted" and we can get started it will probably take several conversations to get it right.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Extreme Flats 20 Problems

Post by TomW1 »

I have been trying to help this builder with his prop and his 40 HP motor. He is totally frustrated and feels like the there was false advertising in the plans. He doesn't want anything to do with the forum despite anything I try to get him to do. His plans right now are to build up the transom 6" and exchange the 40HP for a 70HP motor. If you look at his transom above vs. Richards there is a noticeable difference.

Richard what pitch are you running on your triple cup?
Last edited by TomW1 on Fri Aug 21, 2015 2:40 pm, edited 1 time in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

jacquesmm
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Re: Extreme Flats 20 Problems

Post by jacquesmm »

Tom, thank you for your help.
This builder is free to contact me but it should happen on the forum. I want those discussions to happen in the open.
Many, probably hundreds of those XF20's run perfectly well. If he set up his boat up like those other boats, it should work.
Maybe he is getting bad advice from some outsider?
There were bad feelings between Ken O., one of our first builders who was behind the concept of this boat and some fishing guide on the Florida west coast who by some coincidence is "testing" the boat with this builder and also, selling a similar boat . . .

I like to keep everything open but this may be a case where I have to make an exception.
Capt Dan himself wrote this:
When I was doing my research on building this boat I checked out several. One guide fishes his with a 50-HP Honda and it did fine with 3 people and gear.
Are all our satisfied XF20 builders liars?
Jacques Mertens - Designer
http://boatbuildercentral.com

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Re: prop problems?

Post by jacquesmm »

I changed the title of this thread to prop problems: there are no problems with the XF20. 8)
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