Wild Thing 26" - Tuning help needed.

[Luis Oliveira]

Hi All,

I've built a 26" Wild Thing (scaled down from the 32" original John Finch design) and I am now testing it.

First, I have to say that my experience with boats is very limited. I started with one of those chinese FT009 boats and I got instantly hooked. I modified it a bit, ( added an aluminium rudder, and a 1/8 shaft that allowed me to use some different props) but it's size and solid shaft limited it to around 20mph. By then, wanted more speed, so I used my previous experience in building planes and started building some boats.

I first built a Kep's 2S outrigger hydro (18") which runs very well (around 37mph, but still testing). Then I wanted to build a bigger Mono. I chose John Finch's Wild Thing, but scaled down a bit, I didn't want to go full 32" off the bat, since I am new at this.

I started with a small prop (x435) and worked my way up to the biggest prop I had in hand, which is a grapner k42. It now has decent speed and rides well in glass water, but once I hit my own wakes, it chine walks badly and wants to blow over.

The boat specs are:
Length: 650mm (26")
Weight: 1700g (3lbs & 12oz)
Motor: Boat Rocket 3660 2600kv (28000 rpm unloaded)
ESC: FlyColor marine 90A
Batts: 2x Turnigy 3S 2200mAh in parallel
prop: Graupner K42
strut: 4.8mm (3/16") up - 8.8mm (11/32") from bottom of the keel to center of prop shaft

See it in action here:




I set it up as Mr. John Finch himself advised for starting tuning a new boat: CG at 29%, trim tabs up, strut level.

I now wanted some advice on where to go from here. Should I bet on:
- Another prop? (what is the typical prop for this type and size of boat?)
- move the CG forward?
- drop the trim tabs?
- raise the strut?

I know from what I read that all of the above will most likely improve the handling. What I don't know is where to start. So I would very much appreciate your advice.

Some pics of the boat below. Later on, if someone is interested, I could post a build thread.

https://www.intlwaters.com/media/albums/wild-thing-26.2798/
Thanks in advance.

 

[Terry Keeley]

It's too "loose".

Run the tabs down a bit &/or move the batteries fwd.

Good for you building your own stuff!

 

[Luis Oliveira]

OK, I really need help here. The boat is fast, and can go faster. I have moved the ESC from the port side to the front of the motor. That changed the CG from 28 to 30. But, It still needs help. take a look at https://www.youtube.com/user/OliveiraX.
T

 

[Luis Oliveira]

What I can establish, My boat is getting airborne and getting buut first in the water, Is it? look closely.

 

[John Finch]

Luis,
The 32 inch boat has more weight forward of the transom than the 26 inch boat and It also has more area to stabilize the boat. Look at the transom as a hinge and see that more weight forward of the hinge is going to make the boat less likely to blow off the water even though there is more hull area. I tried the smaller boat like you have and it did not work for me. I would say your boat is actually better than my smaller version and you have done great with it. I am amazed how well it turns left. Normally when we race we have a 330 foot straightaway and a 70 foot diameter turn on each end of the straightaway in IMPBA. Even a large gas boat would have issues with the rollers they would make doing small radius turns like you are making. You could try moving the cg a bit more forward but i feel like the main issue is making all those tight turns causing rougher than usual rollers. You should also not be wading in the water while running the boat. Sorry, had to say that.

 

[Luis Oliveira]

Luis,
The 32 inch boat has more weight forward of the transom than the 26 inch boat and It also has more area to stabilize the boat. Look at the transom as a hinge and see that more weight forward of the hinge is going to make the boat less likely to blow off the water even though there is more hull area. I tried the smaller boat like you have and it did not work for me. I would say your boat is actually better than my smaller version and you have done great with it. I am amazed how well it turns left. Normally when we race we have a 330 foot straightaway and a 70 foot diameter turn on each end of the straightaway in IMPBA. Even a large gas boat would have issues with the rollers they would make doing small radius turns like you are making. You could try moving the cg a bit more forward but i feel like the main issue is making all those tight turns causing rougher than usual rollers. You should also not be wading in the water while running the boat. Sorry, had to say that.

Thank you, Mr Finch. You are an inspiration to all of us boaters. Well, I understand a bigger boat is better to handle higher speeds, but I wanted to start small. And I think I still have not maxed out this one. I have seen boats this size doing 70kph confortably, so that is my goal. From what I have seen, a higher Kv motor with a smaller prop (38mm) is the key to success. Maybe the big props I use(I have gone as high as 45mm) are pushing the boat out of the water a bit too much? Am I thinking right?

 

[john v]

i would try to lower the strut a little bit. not much, maybe1/16''. it might work

 

[Luis Oliveira]

i would try to lower the strut a little bit. not much, maybe1/16''. it might work

That would make it worse. I raised the strut as far as it can go and it got better, (less airborne). Now, the options are: major surgery to the hull to allow the strut to go even higher, or a smaller prop at greater rpm. I will try the second option first, as it is the easier one.

 

[FloridaScaleBoater]

Luis,
The 32 inch boat has more weight forward of the transom than the 26 inch boat and It also has more area to stabilize the boat. Look at the transom as a hinge and see that more weight forward of the hinge is going to make the boat less likely to blow off the water even though there is more hull area. I tried the smaller boat like you have and it did not work for me. I would say your boat is actually better than my smaller version and you have done great with it. I am amazed how well it turns left. Normally when we race we have a 330 foot straightaway and a 70 foot diameter turn on each end of the straightaway in IMPBA. Even a large gas boat would have issues with the rollers they would make doing small radius turns like you are making. You could try moving the cg a bit more forward but i feel like the main issue is making all those tight turns causing rougher than usual rollers. You should also not be wading in the water while running the boat. Sorry, had to say that.

And put some shoes on!

 

[Luis Oliveira]

And put some shoes on!

Will do. I usually wear fishing boots, but that day was in the summer and it was much too hot. Besides, that part of the river is really shallow, the rudder will hit the bottom before the boat gets near me. But that is good advice nonetheless.