Blackbird 21 build thread

[shoboat]

Don,

I think the front boom tube needs to go up more on most outriggers.

Most are running to little of front sponson angle,thus robbing the engine

of the RPM that is required to go very fast. I will share a little number

on my 21 hydro, and believe it or not try 4.3 degrees of angle on your

front sponsons. You will need to run a 46 mm propeller deeper in the

water,but this will be a fast and stable set up if you get the right strut

depth and angle correct.

I Have Tested Many Set Ups,

Mark Sholund

 

[Marty Davis]

Don,
I think the front boom tube needs to go up more on most outriggers.

Most are running to little of front sponson angle,thus robbing the engine

of the RPM that is required to go very fast. I will share a little number

on my 21 hydro, and believe it or not try 4.3 degrees of angle on your

front sponsons. You will need to run a 46 mm propeller deeper in the

water,but this will be a fast and stable set up if you get the right strut

depth and angle correct.

I Have Tested Many Set Ups,

Mark Sholund

Mark:

IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

 

[Don Ferrette]

Mark:
IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

Ok, glad I wasn't the only one who thought that.

 

[Marty Davis]

Mark:
IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

Ok, glad I wasn't the only one who thought that.

Don:

The engine that you sent Norm had a TON of detonation, so I know it was working it's As_ off. I hope it will be stronger when you get it back. It didn't pull much on the dyno, but we found that we had a problem with bearings, so it might have been fine. You will have to try it to see.

I would URGE you to check the setup and be sure that it is perfect. I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level. The setup of that boat is almost identical to what I run and there are a couple great setup tech notes at: http://rcboat.com/setup.htm and another that is digital that I don't remember the link.

Marty Davis

 

[Don Ferrette]

Mark:
IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

Ok, glad I wasn't the only one who thought that.

Don:

The engine that you sent Norm had a TON of detonation, so I know it was working it's As_ off. I hope it will be stronger when you get it back. It didn't pull much on the dyno, but we found that we had a problem with bearings, so it might have been fine. You will have to try it to see.

I would URGE you to check the setup and be sure that it is perfect. I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level. The setup of that boat is almost identical to what I run and there are a couple great setup tech notes at: <a href="http://rcboat.com/setup.htm" target="_blank">http://rcboat.com/setup.htm</a> and another that is digital that I don't remember the link.

Marty Davis

"I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level."
Using the digital level where & how are you measuring the sponsons? B)

Norm told me that every motor run that weekend was reading about 1/2hp down because of the bad bearings on the dyno. He said the motor should work quite well now that all the issues are fixed. We'll see soon enough. Thanks.

 

[Marty Davis]

Mark:
IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

Ok, glad I wasn't the only one who thought that.

Don:

The engine that you sent Norm had a TON of detonation, so I know it was working it's As_ off. I hope it will be stronger when you get it back. It didn't pull much on the dyno, but we found that we had a problem with bearings, so it might have been fine. You will have to try it to see.

I would URGE you to check the setup and be sure that it is perfect. I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level. The setup of that boat is almost identical to what I run and there are a couple great setup tech notes at: <a href="http://rcboat.com/setup.htm" target="_blank">http://rcboat.com/setup.htm</a> and another that is digital that I don't remember the link.

Marty Davis

"I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level."
Using the digital level where & how are you measuring the sponsons? B)

Norm told me that every motor run that weekend was reading about 1/2hp down because of the bad bearings on the dyno. He said the motor should work quite well now that all the issues are fixed. We'll see soon enough. Thanks.

Don:

I found the past tech notes on this subject at: <a href="http://rcboat.com/setup2.htm" target="_blank">http://rcboat.com/setup2.htm</a>

If you have any additional questions, this is an IMPORTANT topic for anyone running this type hull.

Not sure how well it will work without seeing a valid dyno run??? Let us know...

Marty Davis

 

[Don Ferrette]

Mark:
IF you run the strut deeper, isn't that reducing the attack angle of the front sponsons?

Marty Davis

Ok, glad I wasn't the only one who thought that.

Don:

The engine that you sent Norm had a TON of detonation, so I know it was working it's As_ off. I hope it will be stronger when you get it back. It didn't pull much on the dyno, but we found that we had a problem with bearings, so it might have been fine. You will have to try it to see.

I would URGE you to check the setup and be sure that it is perfect. I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level. The setup of that boat is almost identical to what I run and there are a couple great setup tech notes at: <a href="http://rcboat.com/setup.htm" target="_blank">http://rcboat.com/setup.htm</a> and another that is digital that I don't remember the link.

Marty Davis

"I would like to see you try 3.0 on the left sponson and 3.2 on the right with the tub level."
Using the digital level where & how are you measuring the sponsons? B)

Norm told me that every motor run that weekend was reading about 1/2hp down because of the bad bearings on the dyno. He said the motor should work quite well now that all the issues are fixed. We'll see soon enough. Thanks.

Don:

I found the past tech notes on this subject at: <a href="http://rcboat.com/setup2.htm" target="_blank">http://rcboat.com/setup2.htm</a>

If you have any additional questions, this is an IMPORTANT topic for anyone running this type hull.

Not sure how well it will work without seeing a valid dyno run??? Let us know...

Marty Davis

Cool, that's what I thought you were doing, thank you. B)

 

[John Knight]

I just read item #4 on the tech notes and I am confused. The note says the strut angle is "positive" when the rear of the strut is down (more than the front). That drops the front of the hull when running down and tightens it up. And I was always told that it was "negative" and not positive. Have I been wrong in thinking that?

 

[dave roach]

Don

That digital angle finder is the best tool you can have.I wouldn't leave home with out it.

John,Remember The boat is upside down when taking this set up.

Dave Roach

 

[Don Ferrette]

DonThat digital angle finder is the best tool you can have.I wouldn't leave home with out it.

Dave Roach

I've had one for a number of years, just wanted to know Marty's measuring method. B)

 

[shoboat]

Fellas,

If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it.

Have Fun Testing Fellas,

Mark Sholund

 

[Marty Davis]

I just read item #4 on the tech notes and I am confused. The note says the strut angle is "positive" when the rear of the strut is down (more than the front). That drops the front of the hull when running down and tightens it up. And I was always told that it was "negative" and not positive. Have I been wrong in thinking that?

John:

You can call it what you want Really doesn't matter the term.

It is the back of the strut deeper than the front and the reason that you need that on a .21 is that it helps lift the rear of the tub, especially at launch and at the exit of the turns. It is what gets the boat up on the tips of the prop. This is something that MANY Scale Boaters miss. Especially helpful for 1/8 Scale with a lot of weight on the rear of the boat. It is the way to get a boat to come out of the turns hard and launch a high pitch prop well.

With a .45 you need a little bit of angle unless you run a 1600 seried prop, in which case the steep angle of the blade on the hub does the same thing. With the boats above .45, you need zero angle on the strut because the engines have excess HP and will unload easily without shaft angle.

Marty Davis

 

[Marty Davis]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

 

[Tofastformellow]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

85 mph , with a heat race 21 ? , did that 21 have 10hp ? with that low AOA ? what did the boat weigh ?

i completly agree about the AOA thing , if the front sponsons have an afterplane of any kind , they will run quite hapily at rediculous aoa..but it needs groomed water to really be a race winner. rough water does upset the high AOA rule...

as a nextr project on the build . i want to shift the ride point forward on the sponsons shift em forward to the front boom ....to spread the load out futher in the triangle of balance that the 3 point hydro is ..

i figure after high AOA , making the triangle bigger , is the next logical balance exercise.. as is streamlining ...

then again , i could just be a squirel chasing a nut that dont exist.

jason

 

[shoboat]

Marty,

It was not a dig at all, just a general statement. Not many 21 boaters except you and

a few others will ever run even close to 80 MPH with a real low angle of attack on the

front end of their boats. I bet your motor was making some EXCELLENT RPM & HP to

get your boat to run 86 MPH in Trophy Trials. Was the propeller a S-15? Would you care

to share what propeller did this? Curious That Is All?

I am just trying to teach others to try different set ups so you can learn what works

for you or others.

I Will Get Back To Reading,

Thank You For Sharing Your Knowledge Marty,

I have edited that post Marty,certainly no disrespect intended.

Mark Sholund

 

[AndyBrown]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

Mark,

I'm not sure, but I think John Brown still holds the IMPBA 1/3 mile Oval record. Before setting that record John made some passes through the SAW traps and was running about 83 mph.

That boat set up had 3.2 degrees or less.

Marty, It's been a while since I've attended the IMPBA Internats. Which Nats did you run 86 mph at?

 

[Marty Davis]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

85 mph , with a heat race 21 ? , did that 21 have 10hp ? with that low AOA ? what did the boat weigh ?

i completly agree about the AOA thing , if the front sponsons have an afterplane of any kind , they will run quite hapily at rediculous aoa..but it needs groomed water to really be a race winner. rough water does upset the high AOA rule...

as a nextr project on the build . i want to shift the ride point forward on the sponsons shift em forward to the front boom ....to spread the load out futher in the triangle of balance that the 3 point hydro is ..

i figure after high AOA , making the triangle bigger , is the next logical balance exercise.. as is streamlining ...

then again , i could just be a squirel chasing a nut that dont exist.

jason

The boat weighed 3.75 lbs and was running a SAW prop (yes S15 with BBC) for Trophy Trials. No 21 boat will race at that speed that I have ever seen. Most of the very best .21 hydros run in the low 70's set up for heat racing. Engine produced 2.7hp.

Marty Davis

 

[Marty Davis]

Marty,
It was not a dig at all, just a general statement. Not many 21 boaters except you and

a few others will ever run even close to 80 MPH with a real low angle of attack on the

front end of their boats. I bet your motor was making some EXCELLENT RPM & HP to

get your boat to run 86 MPH in Trophy Trials. Was the propeller a S-15? Would you care

to share what propeller did this? Curious That Is All?

I am just trying to teach others to try different set ups so you can learn what works

for you or others.

I Will Get Back To Reading,

Thank You For Sharing Your Knowledge Marty,

I have edited that post Marty,certainly no disrespect intended.

Mark Sholund

Mark:

Stu and I were testing every evening for 2 weeks and I had my boat all ready for the Nats. Andy called and sent me the MAC only a few days before I left for the Nats and I put it in and tested only 2 days. It ran 86.9 and ready for the Nats. I ran that engine and really was happy with the performance. I still run only MAC's in my .21 boat. I have been testing the newest CMB and it is making great power also.

No offense taken at all....

Marty Davis

 

[Marty Davis]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

Mark,

I'm not sure, but I think John Brown still holds the IMPBA 1/3 mile Oval record. Before setting that record John made some passes through the SAW traps and was running about 83 mph.

That boat set up had 3.2 degrees or less.

Marty, It's been a while since I've attended the IMPBA Internats. Which Nats did you run 86 mph at?

Andy:

Sarasota, but as you remember Stevens had the course so screwed up that nobody got correct speed. I based my speed on the testing that I did before I left. The boat won both SAW and Timed Oval and some other guy won US#1 since I had a launch problem in one heat. Can't remember exactly who that other guy was Maybe it was John Brown or somebody like that.

AND, the .21 oval record is an amazing record that probably won't be broken for a while.

Marty Davis

 

[AndyBrown]

Fellas,
If you a deeper strut yes it will lift the transom higher on the boat,but it

will also increase the propeller efficency. The goal is to not rob HP to

get the boat to ride light on the water, correct? If you raise the front angle

of attack more and the back end levels this out with a deeper propeller

setting you will be flying pretty neutral on the water. This is just a different

way to achieve a good fast heat racing boat. There are a lot of different ways

to achieve this. One wise boater told me to run as much: angle,timing,and nitro

% that you can get away with. If 3.2 degrees works for you run it. I doubt you

will ever run 75 to 80 MPH that way though.

Have Fun Testing Fellas,

Mark Sholund

Mark:

I agree with everything you said except the last dig.

FYI, at the Internats several years ago, I ran 86mph with my heat race .21 boat in Trophy Trials, so you are incorrect with this statement. Angles on the sponsons were exactly 3.0 and 3.2.

There ARE many ways to get there though, you are correct about that.

Marty Davis

Mark,

I'm not sure, but I think John Brown still holds the IMPBA 1/3 mile Oval record. Before setting that record John made some passes through the SAW traps and was running about 83 mph.

That boat set up had 3.2 degrees or less.

Marty, It's been a while since I've attended the IMPBA Internats. Which Nats did you run 86 mph at?

Andy:

Sarasota, but as you remember Stevens had the course so screwed up that nobody got correct speed. I based my speed on the testing that I did before I left. The boat won both SAW and Timed Oval and some other guy won US#1 since I had a launch problem in one heat. Can't remember exactly who that other guy was Maybe it was John Brown or somebody like that.

AND, the .21 oval record is an amazing record that probably won't be broken for a while.

Marty Davis

Marty,

I'm getting old and I guess my memory fails me sometimes, but I didn't think you got a time in SAW. I seem to recall that your boat died on the first launch attempt. It was retrieved and Mark Grannis gave it another all out super launch and it died again.

Maybe I've forgotten. Do you remember what kind of speed you ran on John Stevens' messed up course?