Tunnel Set Up, Props & Engine Tuning

[kesso2118]

I had a thread going in the General Boating Forum about Glow Plugs and I managed to get into talking about props, engine tuning, pipe length, etc which I'm very interested in, so I though I had better start a new topic to focus the inputs on the REAL ISSUES!

Poolschool (Gino) raised some good questions on the previous thread about my quest to "dial in" my TS2/CMB RS .21 Combo with a SPP NR21OB Pipe.

I have broken in my engine running on the factory settings for both low end and high end needles, using 20% Nitro over 5 tanks of fuel (approx. 40ozs). I followed the TS2 balancing and engine set up guidelines as best I could e.g. engine height had the prop shaft centreline 1/8th inch above the sponson bottom and angle neutral. I had 4 ozs of lead in the front of the cowling and cg at about 9 1/4" from the transom. The prop was an ABC 40/53 with 3.9" of cup. The boat and engine were running reliably but not fast.

My first steps to get some speed was to try leaning off the mixture and restricting water cooling a little bit each time. I started to get some improvement in speed and the boat was still handling well.

I then changed the fuel to 40% Nitro with 18% Oil ( 16% Klotz & 2% Castor). The boat and engine continued to run well and I continued leaning the mixture & restricting the water. The engine came on pipe once and the boat took off "like a dog kicked in the bum". The nose came up and it wanted to fly off the water. I was now getting excited!!

Unfortunately, on that one run where it came on pipe I lost the flywheel and couldn't continue testing until I got a new one. This is where Gino's question is very important to me:

"...also noticed that you ran on 20% then swapped to 40% nitro, whilst "leaning" on the motor. Isn't it a general rule that you richen as you go up in nitro content??? Anyone feel free to correct me as I'm always willing to learn....."

While fitting the new flywheel, I knew the boat was going to be fast next time out, so I checked the set up and noticed I had a bit of positive trim on the engine. I set this back to neutral to ensure it wouldn't blow off the water and added an extra 1/2 oz of lead in the cowling slot.

However, my next outings were less than exciting, the boat is handling well but I'm not getting any BIG revs or speed. In fact the speed and revs increase when I go into a corner but then die off going down the straight as I open up the throttle. I burnt out the CMB Glow Plug, that came with the engine, on Sunday so I think I must be getting too lean on the mixture.

Tim Duggan and Mark Sholund have given me good advice and offers of assitance which I appreciate and will follow e.g. try the 1440 b/c I already have and experiment with Pipe Length.

So, this might sound more like a "Kesso2118 Blog" but if I keep it updated it might turn into a useful thread for other Newbies like me, to get info on "dialling in" their boats.

Please feel free to contribute useful info.

Thanks,

James

 

[Tim_Duggan]

James,

What I'd suggest you do first is establish the static balance or CG point of the boat RTR less fuel. It is the distance from the trailing edge at which the boat balances at. I'd suggest aiming for about 28% or 8.4" from the trailing edge of the sponsons. Use this info to get the right amount of lead in the boat. (this is only a starting point - it will get adjusted at the pond)

Then I'd set the propshaft angle as close to zero as possible or with a tiny amount of negative on it,say less than 1 degree, and the bottom of the propshaft level with the bottom of the sponsons. (this also is only a starting point - it will get adjusted at the pond to suit the prop) These things can all be done at home - before you go to the pond.

What I'd do at the pond with a pipe'd tunnel;

Start with a known prop for the engine that is on the smaller side - in this case I'd suggest a X438 - I can loan you one so don't rush out and buy one. The smaller prop lets it get on pipe easier and will help in diagnosing if something else is stopping it peaking out on the pipe.

Also, use a new glow plug - preferrably something with some heat in it like a K&B 1L, or an McCoy MC59 and start off with a very rich sounding needle on the bench. It's way better to start off rich and work down to a needle than to start off too lean.... unless you enjoy being in the rescue boat and killing glow plugs! (Gino was right by the way - more nitro % requires the needles to be wound out anticlockwise to allow more fuel thru.) Using a new plug allows us to "read" it after a run to get an idea on the mixture and the state of the engine.

Now assuming all of that works so far;

Gradually raise the engine height a small amount at a time until you start to induce bouncing like mine did on Sunday, then back it down until the bouncing goes away.

If the hull gets too flighty like it's going to blow over backwards near the end of the straights - add weight to the CG (not the nose!) Remember tunnel hulls are supposed to "fly" - the aim is to make it as stable as possible without running too "wet". No easy feat but when you get it close you will know!

As for the pipe. If it won't get on pipe, lengthen it 1/4" at a time until it does. If it comes on pipe really easy, fit a bigger prop, or shorten the pipe to gain more rpm's. Again it's about a balance - I prefer to use a slightly smaller prop than the biggest the engine can pull and then shorten the pipe accordingly.

 

[kesso2118]

Thanks Tim, that is great info and a good plan that I can understand. I'll ensure we have those settings and I'll take you up on the offer of the X438.

Regards,

James

 

[Mike Larson]

Hey James.... Tim's info rocks.... listen well...... Tuning a tunnel hull is a great test of patience... I actually have years on a couple of mine,..... Main point of interest is to only change one thing at a time, measure, mark, and gain information, then move to a different change if needed, once you gain a base line set up, modest speed, good handling, etc, then move on to fine tuning props, pipe/motor, balance, and all the other great stuff thats soon to drive you insane..... My mod stuff likes the x640 cut to 38mm, reduced dia 442's, 220's Sholund is the man, he knows my numbers,.... Get some test time, and get some more, ive seen the potential of the hull, its there, and you'll find it.... just takes time..... Mike

 

[GRoth265]

Tim is giving you some good information the only thing I would add is only do one thing at a time otherwise you don't know what worked. When a piped engine is ( on the money) it will pull the coil out of the bottom of the plug after a good hard run. You can usually put another run on it, But when it counts it's a plug a run. Go to a x440 or reduce the pitch on the 1440 to 3.6" and get the motor on the pipe (sounds like your to short) then work with the needle and pitch. The motor angle should stay very close to zero +/- 1/4 degree. Lead is the final trim to keep the boat from bvlowing off. Hope this Helps Greg

 

[shoboat]

James,

FYI,

Try to run the least amount of cup in the trailing edge of the propeller. RPM is what will give

you the speeds that we are all looking for.

We found through a lot of testing that 3.46" of cup on the 1440 B/C was where it worked the best.

Anymore cup and the boat usually slowed down in the turns and the lap times suffered.

Have Fun Testing,

Mark Sholund

 

[Ralphie]

Hi

Always lots of talk about prop angle + & -

I'm new at these tunnel boats and would like to know how you measure, is there a gauge you use of just "eye ball".

1/4 , 1/2 1, 2 degress any way of measureing ? Or just "trial & error".

Thanks as always for your help.

Ralph

 

[kesso2118]

TS2/CMB RS .21 Update

Thanks to everyone for their input last week. I had good testing session yesterday with some reasonable progress.

I started the day with a new McCoy MC59 Plug and X437/3 prop ( the smallest I had). I was still running 40% nitro and 4.5 ozs of lead in the front with a cg of 9.25 inches from the trailing edge of the sponsons. There was no real change in performance.

I gradually made the top end mixture richer until it was clear that it was dropping performance. I then went back a couple of clicks to where it was most responsive.

The boat was still displaying its "normal" characteristics i.e.

* Engine always starts with one hit from the starter

* Boat never stalls when launched and accelerates onto the plane quickly with minimal cavitation

* Tends to run slow for the first lap or two and then performs better as it warms up

* Speeds up in turns and loses revs on the straight at full throttle

I tried small 2 blade ( an old JG E20 about 38mm) but it cavitated and wouldn't get on the plane.

I then tried the 1440 b/c Shoboat prop and it seemed to increase acceleration and general responsiveness, however, the boat continued to lose revs down the straight.

The water conditions varied from choppy, to fine wind ripple and the boat continued to handle the choppy conditions well. It tended to run faster into the wind.

I then tried a tiny bit of positive trim and while it allowed the boat to lighten up slightly there were still no high revs down the straight.

I then raised the engine height slightly. Still no dramatic increase in speed but the boat was starting to fly a bit off the waves.

I then tried to lengthen the pipe and managed to move the coupler about a 1/4 inch further out on the header.

The boat then started to show more performance down the straight. It was beginning to hold the revs down the straight that it had built up in the turn. It was also starting to get a bit flighty as the water had a good wind chop. YAHOO!!

It was at this time I found I had used up all my fuel (about 40 ounces) and had to "call it a day" and go home.

I was very happy that I got to try a number of things and while there is still a lot to do it looks like varying pipe length will be something to focus on next week at the pond.

 

[Tim_Duggan]

* Tends to run slow for the first lap or two and then performs better as it warms up

This can be a characteristic of carbon fibre pipes on outboards. You learn to compensate for it..... also, did you get rid of the water cooling like I suggested?

I then tried to lengthen the pipe and managed to move the coupler about a 1/4 inch further out on the header. The boat then started to show more performance down the straight. It was beginning to hold the revs down the straight that it had built up in the turn. It was also starting to get a bit flighty as the water had a good wind chop. YAHOO!!

Which prop was this with James?

I was very happy that I got to try a number of things and while there is still a lot to do it looks like varying pipe length will be something to focus on next week at the pond.

If you were testing at Narrabeen - don't be surprised if you find it's different at Penrith! Also, You have little chance of getting the boat trimmed correctly if you are trying to make adjustments and test on choppy water.

Also, I have another pipe that acts a little longer than the pipe you have - if you don't have enough header to lengthen the pipe further, this might be the next option to try.

Tim.

 

[kesso2118]

Tim,

Question 1 - I haven't disconnected the water cooling yet

Question 2 - The 1440 b/c was on it when I lengthened the pipe

I'm really looking forward to next Sunday at Penrith where hopefully, we'll get some reasonable water for more accurate testing. I'll have to get there early!

Thanks,

James

 

[shoboat]

James,

How much cup on the 1440 B/C? 3.21",3.33",or 3.46"?

It will make a big difference,I think it may have too much cup in it if it is that

sensitive on the pipe. Your engine is still too cold for maximum performance.

Have Fun,

Mark Sholund

 

[aaron alberico]

James,

get that heat into the engine!!!!

makes a big differents!

these guy's no what there talking about [i hope] lol

regards Aaron

 

[Tim_Duggan]

James,

I'll be there at around 8am. No boats on the water until 9am but that gives time to get set - up.

Ditch the water cooling - it won't hurt the engine not having it there. If anything, running it too cold will do more harm than good. Gino's engine (also a CMB 21RS) which is on a lawless drive still comes back too cold for my liking with no water going thru the head at all!

Think of heat as free horsepower! Building up sufficient heat in an O/B can be a real challenge because of the leg being in the water and drawing the heat out of the engine, but it's possible! On mine, I'm thinking of putting a gasket between the PTO and the leg to try and get the engine hotter. Involves some machining on a TT to maintain the gear mesh however.

 

[kesso2118]

Thanks Guys.

We'll definitely try it without the cooling on Sunday.

Mark,

I'll confirm the cup when I get home tonight and get back to you.

Regards,

James

 

[kesso2118]

James,

How much cup on the 1440 B/C? 3.21",3.33",or 3.46"?

It will make a big difference,I think it may have too much cup in it if it is that

sensitive on the pipe. Your engine is still too cold for maximum performance.

Have Fun,

Mark Sholund

Mark,

My 1440 b/c has 3.33" of cup.

Regards,

James

 

[Gator 340]

Hey kesso just bring that boat to the tunnel race in Charlston SC in march I promiss you by the time you go home that thing will either be a rocket or you will have baught a new boat That goes for any of you guys having set up questions come to the tunnel race and get advice from the best tunnel guys in the world thats right the world.

 

[kesso2118]

Hey kesso just bring that boat to the tunnel race in Charlston SC in march I promiss you by the time you go home that thing will either be a rocket or you will have baught a new boat That goes for any of you guys having set up questions come to the tunnel race and get advice from the best tunnel guys in the world thats right the world.

Gator 340,

That sounds like a great offer, however, it might take me a while to drive there, because I'm not sure which road to take after I leave Sydney, Australia. Do I take the left or right at Albequerque, I always forget which one......?

Regards,

James

 

[John Knight]

Hey kesso just bring that boat to the tunnel race in Charlston SC in march I promiss you by the time you go home that thing will either be a rocket or you will have baught a new boat That goes for any of you guys having set up questions come to the tunnel race and get advice from the best tunnel guys in the world thats right the world.

Gator 340,

That sounds like a great offer, however, it might take me a while to drive there, because I'm not sure which road to take after I leave Sydney, Australia. Do I take the left or right at Albequerque, I always forget which one......?

Regards,

James

You already have your guide - Kris Flynn - he is coming. Hitch up with him and let's have an Aussie party here in South Carolina!

 

[Gator 340]

Hey kesso just bring that boat to the tunnel race in Charlston SC in march I promiss you by the time you go home that thing will either be a rocket or you will have baught a new boat That goes for any of you guys having set up questions come to the tunnel race and get advice from the best tunnel guys in the world thats right the world.

Gator 340,

That sounds like a great offer, however, it might take me a while to drive there, because I'm not sure which road to take after I leave Sydney, Australia. Do I take the left or right at Albequerque, I always forget which one......?

Regards,

James

There you go like knight said hook up with Flynn and come on over.

You already have your guide - Kris Flynn - he is coming. Hitch up with him and let's have an Aussie party here in South Carolina!

 

[Kris Flynn]

yeah what they said...Gino, Mark, made up your minds yet?