Boat Builder Central - Builder Forums

I do not know how to attach pictures. If someone would be king enough to provide instructions I will attach the pics of the launch.[/img]

You have to start a gallery, then upload them. See the FAQ section of the gallery...

http://gallery.bateau2.comfaq.php

Please try this first. If are unable to get the get them up, then email them to me and I will post a couple in my gallery.

Joel

I am unable to post pictures of the XF launch but I shall do my best to describe it, both the good and the bad. The boat went in the water easily and floated. The 1st time I poured the coal to it I was immediately hit in the back of the head by a plume of saltwater. I turned around to see what had happened and got hit the face by the same plume. I am running a Tohatsu 50 hp with an 11.1x11 prop. I have it mounted on a Vance jack plate. What is happening is the water exiting the tunnel is hitting the bottom of the jack plate and shooting up between the motor and the jack plate. Very little water is getting to the prop which explains the 5,000rpm 12 mph performance. Has any one used a Vance jack plate? My next step is to cut the bottom of the jack plate off below where the motor mounts and try to remove the “scoopingâ€

See this post here:
http://gallery.bateau2.com/forum/viewtopic.php?t=12352

Someone is trying to help you, but can't log in right now. I know of what you're describing too, but don't have that problem on any of my tunnel boats. What this post suggests will surely help.

I think what you need to do is raise the motor. It is my experience that you're getting water pushed back off the front of the lower unit because the motor is too low in the water. It may not be the case with your boat though. I think Hunch might have had a similar issue with his XF-20.

Email the pics to Shine or me and we'll get them posted up.

Tim

And try first with engine lower or higher. Then move it a little bit at a time. That will show you when the flow begins to hit the jackplate.
It is due to the shape of the jack plate but there is a solution. Some have build a deflector to mount on the transom, it pushes the water down.

I sent an image of the Tar Heel XF 20 to Shine.

Diesel

Here you go. Nice looking boat......

i definitely would like to see more...id like to see something closeup of your jackplate problem...your boat looks great

I think Hunch was using the same jack plate and had the same issues...I think....

Here is a deflector on another S&G boat





It's for a jet, but same principle would apply.

Good looking XF20...send more pics

Wow... you people are just as crazy as i am. searching the web at every conveniance for obscure boat related facts and photos... this website truely is a "force multiplyer". I get the benfit of all of this searching, I just can't get over that. The pics that are posted with some replys are an almost constant reminder that this is the best bee-hive on the web.

Put theTar Heel back in the water on Sunday. I had raised the motor up as high as it would go and still have water available to the water intake. The Jack plate cleared the water exiting the tunnel but the prop was above the clean water exiting the tunnel. My next step will be to shape the bottom of the Jack Plate to eliminate the interference of the water flow to the prop then lower the motor so it is running in clean water.

Question; the jack plate has a 6.5â€

If this is a manual jackplate, which I think is what we are talking about, a good starting point is with the anti-ventilation plate even with the top of the tunnel. You will typically be able to raise the motor slightly above this level with some fine tuning and a good, cupped prop.

Post some pictures.

Tim

is that a long shaft motor(21") or short shaft(15")....and what kind of measurement do you have from top of tunnel to top of transom...i ran a 90 on a tunnel boat(very different design) and i needed lots of setback to get my motor running high...i had aroun 8 1/2 inches of setback...but that may not be your problem...you should not have to modify your jackplate...

Yes this a manual jack plate. If I have a starting point (which I now have) and could get the boat to plane I figured I could then move the motor up a little or down a little to find the "sweet spot". Thanks for the help. I dont know how to post pictures but I have a website.

http://timmurphyboat.bravehost.com/

Tar Heel wrote: What is happening is the water exiting the tunnel is hitting the bottom of the jack plate and shooting up between the motor and the jack plate.

Sorry for not responding sooner, I was out fishun'

I had the same problem with a Detwiller plate I purchased from Pratt. The lower bar protruded into the "hump" of water at the tunnel. No modification or height adjustment would fix the problem. I'm using the original version of the xf plans with the 15" dim over the tunnel top.

I sold the Detwiller on eBay and got a CNC which has no horizontal bar and which works like a charm, although the side frames do drag a little with the plate all the way down. The sweet spot on my XF puts the cavitation plate approximately 2" above the tunnel top, using a 13.5 x 15 x 4 blade cupped PowerTech prop, on a 110 hp Evinrude.

http://www.frohboseandbeers.com/zoo/HPIM0139.jpg

This pic shows the jack plate in the lowest position. The CMC has a 6" range.

I wouldn't recommend a manual plate on the XF20. She's a tempemental bitch and weight sensitive to get up on plane without squat. But then again my boat is very heavy compared to most XF20 builds.

Your boat looks great. Dig out a kidney belt and enjoy the best fishing platform you ever fished on.

Hunch,
Thanks for the reply! How much of a setback does your CNC plate have?

Tar Heel wrote:Hunch,
Thanks for the reply! How much of a setback does your CNC plate have?

6" setback. BTW I couldn't be happier with any other jack plate. The CMC is inexpensive and has worked flawlessly for the last year.

Its all self contained so it makes for an easy install.

Tight lines

Hunch

Thanks Hunch,
This gives me a starting point. I can't seem to get my head around the concept of raising the motor to correct cavitation. I have cut the bottom of the jack plate down and am sure it will be out of harms way. My plan is to try it again on Sunday. I f I can get er on plane I will feel like I am winning this year long battle with building a boat. The next obstacle will be catching a fish on it.

Tar Heel wrote:Thanks Hunch,
This gives me a starting point. I can't seem to get my head around the concept of raising the motor to correct cavitation. I have cut the bottom of the jack plate down and am sure it will be out of harms way. My plan is to try it again on Sunday. I f I can get er on plane I will feel like I am winning this year long battle with building a boat. The next obstacle will be catching a fish on it.

Put your cavitation plate at 2" above tunnel top to start. This should be a good base line to work from.

The lower the cavitation plate the easier it will be to get on plane. ( as long as the plate aint dragging )

The higher ya raise the motor the more likely you will cavitate in turns but the tunnel outflow will prevent cavitation when goin straight and you will draw less and run more efficiently. Look for a nice clean wake.

I cruise at around 3800 - 4200 so when I turn my tach may hit 5200 or so if I dont feather the throttle.

The xf20 doesnt really turn. It sorta skids around like an airboat, so be careful in close quarters.

I need help!! I am still having a cavitation problem. I removed the jack plate from the boat and shaped it so it no longer interferes with the flow of water exiting the tunnel. I launched the boat this evening and started out with the engine at its lowest position. I then began stopping and raising the motor ½â€

I'm running a 50 yamaha with a 4 blade cupped prop from power tech.I believe the prop diameter is 11.25. Have you tried some different props?I had no trouble getting up with any of the props I tried. my problems showed up when I attempted to turn. I know tyhis sounds like a stupid question but have you checked the hub on your prop? It happened to me once on a brand new prop I would put the throttle down and it would grip to about 2500 rpm then the hub would let go.

Brian,
It is not a stupid question and no I have not cheched the hub. It is a new prop, I will check it tomorrow and post the results.
Thanks for the speedy reply

So you still can't do more than about 12 mph?

I don't think your prop is too narrow of diameter, but I do know you can get a specially made prop for that motor that is a 13" diameter. I have a friend running one on a worked over 40 Tohatsu on an aluminum tunnel hull. I could get you details, but we're talking about a $400 prop for a 50 hp. Let me know.

I would definitely have your hub tested. It could be your problem.

Can you look over the transom when on plane (or at max RPM) to see what the water is doing exiting the tunnel? Can you see the anti-ventilation plate and/or prop blades?

How about when you're sitting still or at idle. Where is the prop and AV plate then with respect to the water's surface?

Hope we can help...

Very Strange
Do you have electric trim control and if so how does it affect the performance? It has by far the most impact on how fast I can get on a plane. The jack plate height has almost no impact unless I have it too high and the prop cavitates.
If it's manual trim it could either be way too far in and pushing the bow down or way too far out pushing the stern down?

Tar

I had the same problems with my '06 Tohatsu TLDI 50 and my bet is on the dia being to small for the conditions you're running in. I found that a smooth glass water surface yeilded much better performance than water with any kind of chop. I think air that is getting passed under the flat bottom is getting mixed with the water in the tunnel. This results in a less dense mix getting supplied to the prop out of the tunnel. I can go into this more later and have some questions for Brian about his tunnel and the PT prop. I purchased a cupped 4 blade prop from PT that helped but certainly didn't solve the problem.

I live in St. Cloud and can get together with you to compare notes if you like. Give me a call at 407 957-9553.

Brian did you build the tunnel per plans specs and what is the part # for the PT prop?

Tar heel

If you can't get a new prop Get the prop re-cupped by a good prop shop.
or find a shop that will give you a few props to try so there's no hit or miss.

Hunch

the model # on that prop is swc4rpy850 10 pitch. The prop is not perfect, at wide open throttle I'm around 28 mph at 5400rpm which is pretty good however my turning performance is lacking. I tried several different props ,both power tech and others and the power tech was by far the best.I have no problems out of the hole or in rough conditions my only problem is losing bite in turns.

From my experience with the tunnels you will get some cavitation. Even the PH15 cavitated some in sharp turns.Running a 4 blade. power tech prop on it.

Thanks for helping out T/H. I stopped by his shop last night and after we looked things over. It appeared that the washer in front of the prop was incorrect. Juggled the parts, torqued the prop nut and the boat felt like it hit warp speed to me.

I am sure he will provide more specific information to all of you that assisted with the issue.

Diesel