Is the OB class doomed?

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LohringMiller said:
A picture to show the motor better. It's a real outboard.

Lohring Miller
View attachment 328459
Click to expand...
A few years ago I built two custom lower units similar to the one shown in your picture. I liked it a lot because it moved the C/G forward and helped the weight distribution of the boat but by fixing one issue it created another. Even with a perfectly balanced prop, as you increase the distance between the mounts and the propeller, you also increase the props ability to to transfer its vibration resonance from the propeller blades striking the surface back into the lower unit. this was a large prop and that made it even worse.

When you lean the engine forward and stretch the prop way behind the mounting location, the lower unit acts like a tuning fork and amplifies any vibration causing failures with fasteners and cracking things that normally never fail. It was fun but was another learning curve. If I ever make another one I will keep that in mind. I most likely made my lower (not knowing at the time) that was perfectly resonate with the RPM range we were hitting.

If you make a custom stretched and laid down lower unit and you don't have these issues you were lucky. DCP_4236.JPG
 
Carl Van Houten said:
A few years ago I built two custom lower units similar to the one shown in your picture. I liked it a lot because it moved the C/G forward and helped the weight distribution of the boat but by fixing one issue it created another. Even with a perfectly balanced prop, as you increase the distance between the mounts and the propeller, you also increase the props ability to to transfer its vibration resonance from the propeller blades striking the surface back into the lower unit. this was a large prop and that made it even worse.

When you lean the engine forward and stretch the prop way behind the mounting location, the lower unit acts like a tuning fork and amplifies any vibration causing failures with fasteners and cracking things that normally never fail. It was fun but was another learning curve. If I ever make another one I will keep that in mind. I most likely made my lower (not knowing at the time) that was perfectly resonate with the RPM range we were hitting.

If you make a custom stretched and laid down lower unit and you don't have these issues you were lucky. View attachment 328461
Click to expand...
Carl Van Houten said:
A few years ago I built two custom lower units similar to the one shown in your picture. I liked it a lot because it moved the C/G forward and helped the weight distribution of the boat but by fixing one issue it created another. Even with a perfectly balanced prop, as you increase the distance between the mounts and the propeller, you also increase the props ability to to transfer its vibration resonance from the propeller blades striking the surface back into the lower unit. this was a large prop and that made it even worse.

When you lean the engine forward and stretch the prop way behind the mounting location, the lower unit acts like a tuning fork and amplifies any vibration causing failures with fasteners and cracking things that normally never fail. It was fun but was another learning curve. If I ever make another one I will keep that in mind. I most likely made my lower (not knowing at the time) that was perfectly resonate with the RPM range we were hitting.

If you make a custom stretched and laid down lower unit and you don't have these issues you were lucky. View attachment 328461
Click to expand...
That's definitely a Nelson motor
 
Mike ran a stock, air cooled Mac 3.5 standard rotation engine. We had no particular vibration problems. The boat has several features that Mike developed over years of testing that made his SAW boats fast and stable.

The aft main wing coupled with forward sponsons lifts most of the boat's weight out of the water and gives great longitudinal stability. Air trapped sponsons lift much of the remaining weight out of the water while creating troughs that help hold the run straight. These design features really helped on heavier gas boats. We got a 3 mph increase with air trapped sponsons on the 110 mph gas record holder. The first runs with the outboard hydro showed that the wing was too big so we took a little off the ends on the final boat.

Balancing air and water lift is critical for high speed success. Tunnels have this problem in spades. Any design has a maximum speed where the tunnel lift is too high. Hydros can get around this but it takes an understanding of the forces involved. Mike has the best feel for boat design of anyone I've worked with. It was developed over years of trying everything we could think of. The fact that no one has beat this O/B hydro record is evidence of this.

Lohring Miller
 
LohringMiller said:
Mike ran a stock, air cooled Mac 3.5 standard rotation engine. We had no particular vibration problems. The boat has several features that Mike developed over years of testing that made his SAW boats fast and stable.

The aft main wing coupled with forward sponsons lifts most of the boat's weight out of the water and gives great longitudinal stability. Air trapped sponsons lift much of the remaining weight out of the water while creating troughs that help hold the run straight. These design features really helped on heavier gas boats. We got a 3 mph increase with air trapped sponsons on the 110 mph gas record holder. The first runs with the outboard hydro showed that the wing was too big so we took a little off the ends on the final boat.

Balancing air and water lift is critical for high speed success. Tunnels have this problem in spades. Any design has a maximum speed where the tunnel lift is too high. Hydros can get around this but it takes an understanding of the forces involved. Mike has the best feel for boat design of anyone I've worked with. It was developed over years of trying everything we could think of. The fact that no one has beat this O/B hydro record is evidence of this.
Click to expand...
81.5 mph?...With a custom made lower unit, custom made hydro, a high timed engine and tuned pipe? I would think that record should be in the mid 90's. In 2005 This was a good time but a round track Zippkit hydro holds the IMPBA O/B Hydro record within 5mph of this record and the 3.5cc inboard record is now 41.1 mph faster than that time. This record needs to be revisited soon because I am certain that their is much more left on the table. Where is that boat? Ya'll get it back out and give it a go.
 
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According to the IMPBA web site the IMPBA B outboard hydro record is 76.5 mph. The IMPBA B tunnel record is 68.8 mph. The motor was a stock out of the box MAC 21. At the time the 3.5 riggers were running under 100 mph, but Mark Grim pushed that NAMBA record over 100 mph in a great competition with Steve O'Donnell. Mike is now in England and has moved on to Offshore racing and fun model boats

Lohring Miller
 
LohringMiller said:
According to the IMPBA web site the IMPBA B outboard hydro record is 76.5 mph. The IMPBA B tunnel record is 68.8 mph. The motor was a stock out of the box MAC 21. At the time the 3.5 riggers were running under 100 mph, but Mark Grim pushed that NAMBA record over 100 mph in a great competition with Steve O'Donnell. Mike is now in England and has moved on to Offshore racing and fun model boats

Lohring Miller
Click to expand...
I was hoping Mike would make another run. Yes, you are correct the IMPBA current record is 76.5 mph (within 5 mph of Mike record) set by David Hall. With all that has been learned and developed since 2005, someone should go after these O/B records soon.
-Carl
 
Before I got Covid, I've been trying to get a 34" XT-460 to run with one of the new TenShock motors on a K&B 7,5 lower unit. The hull I'm running has won and placed at several NAMBA Nationals. It's run everything from a 3.5 mod engine to an 11 cc mod engine. I'm running the same balance point as the 11 cc version did and the weight is similar.

However, the highest speed I've radared an XT-460 was 61 mph driven by Frank Crocket in a heat race. In the distant past I held the 11 cc mod SAW record at 57 mph with an XT-460 . This boat is running over 70 mph as calculated from the motor rpm and x450 prop. The motor could easily run a bigger prop, but the boat can't handle the x450. I still can't keep the boat on the water, but the cornering is OK. I'll work on it more at the NAMBA Nationals, hopefully with some help from the NW tunnel guys.

I also have been thinking about an outboard hydro. Carl and I have been exchanging drawings. I think a big problem is the P length limit. It's starting to result in hard to control little hulls in several classes. Brian Buaas had the thought that an 8S limited class can be inexpensive with the current equipment. He is testing this on a Mutt sport 40 I loaned him.

Lohring Miller
 
I will still be tinkering and working on competition R/C model boat designs of some kind as I have always done but after a lot of thought this is a turn that I needed to make. Hopefully a new manufacturer will step up and build a new line of nitro powerheads that are reasonably priced soon.

If you need anything, I can be found at: [email protected]

Thanks,
- Carl
 

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Carl Van Houten said:
I will still be tinkering and working on competition R/C model boat designs of some kind as I have always done but after a lot of thought this is a turn that I needed to make. Hopefully a new manufacturer will step up and build a new line of nitro powerheads that are reasonably priced soon.

If you need anything, I can be found at: [email protected]

Thanks,
- Carl
Click to expand...
Carl thnx for all you've done in the hobby. As we age our priorities change and life goes on.
 
Hi:
I have been competing in this beautiful category of 3.5cc Tunnels outboard for some time (well, a few years) and I have always used OS engines, both the old one and the latest version with the longer silencer.
I have seen my colleagues competing with K&B engines, with Novarrossi engines, with OS engines modified by Rody Roem (a marvel, really) and I have a conclusion that comes from the humble experience gained:
It is easier to MODIFY a stock 3.5cc on-road car engine than to design and manufacture a completely new 3.5cc Glow engine.
Why not orient the supply of engines from that angle?… not BUILD an engine from scratch, but USE A GOOD 3.5cc on-road BASE and MODIFY it to be used in Outboard Drive Systems… i.e., TFL outboard Stern Drive system, O.S. Outboard Unit Assembly 21XM V2, or similar
Could this be a cheaper option than building an engine from scratch?… Any engine builder/preparator out there who can give us their opinion?
 
Julio Almazan said:
Hi:
I have been competing in this beautiful category of 3.5cc Tunnels outboard for some time (well, a few years) and I have always used OS engines, both the old one and the latest version with the longer silencer.
I have seen my colleagues competing with K&B engines, with Novarrossi engines, with OS engines modified by Rody Roem (a marvel, really) and I have a conclusion that comes from the humble experience gained:
It is easier to MODIFY a stock 3.5cc on-road car engine than to design and manufacture a completely new 3.5cc Glow engine.
Why not orient the supply of engines from that angle?… not BUILD an engine from scratch, but USE A GOOD 3.5cc on-road BASE and MODIFY it to be used in Outboard Drive Systems… i.e., TFL outboard Stern Drive system, O.S. Outboard Unit Assembly 21XM V2, or similar
Could this be a cheaper option than building an engine from scratch?… Any engine builder/preparator out there who can give us their opinion?
Click to expand...
I AGREE 100%!
 
Julio Almazan said:
Hi:
I have been competing in this beautiful category of 3.5cc Tunnels outboard for some time (well, a few years) and I have always used OS engines, both the old one and the latest version with the longer silencer.
I have seen my colleagues competing with K&B engines, with Novarrossi engines, with OS engines modified by Rody Roem (a marvel, really) and I have a conclusion that comes from the humble experience gained:
It is easier to MODIFY a stock 3.5cc on-road car engine than to design and manufacture a completely new 3.5cc Glow engine.
Why not orient the supply of engines from that angle?… not BUILD an engine from scratch, but USE A GOOD 3.5cc on-road BASE and MODIFY it to be used in Outboard Drive Systems… i.e., TFL outboard Stern Drive system, O.S. Outboard Unit Assembly 21XM V2, or similar
Could this be a cheaper option than building an engine from scratch?… Any engine builder/preparator out there who can give us their opinion?
Click to expand...
I`ve been doing that exact thing for more than a decade. Using car engines mounted in a gearbox that bolts directly onto an existing lower.
It allows the use of every car engine available as long as they have the standard bolt pattern (which most of them have)
No engine mods needed, well maybe add a waterjacket in very hot conditions. You can even use the stock carb if you`re not as picky as I am 😅 The pricetag on an assembly like this depends very much on the engine you want to use. But even if you choose one of the high end on-road engines, I believe it will be cheaper than a new designed outboard.
Or you can go with a direct drive solution, then you only need a bracket basickly, which is allready available.
I have designed a new 7,5 and 15 cc outboard, complete engine and lower, so I have a clue about the amount of time you need to put into it. Then you have to make prototypes and do all the needed testing and probably revisions prior to put it in production, it is hundreds of hours spent before you can even concider a production run.
I decided to put the project on ice until further, maybe I will pick it up some day...
Regarding the OS XM engine, I received a notification earlier this year that OS will discontinue the outboard after the current stock has been sold out, at that time they only had a few engines left. However, I have not seen or heard anything yet about the engine being discontinued.
 
Mounts for standard engines to outboard lowers have been around a long time. However, none of this is as cheap and easy as the old K&B outboards. Today, I believe the future of outboard racing is electric power. You can buy complete units in either 3.5 or 7.5 size from Hyperperformance for $300. See: http://hyperprod.bizhosting.com/complete_electric_outboard.html
If you want a hotter setup, get their conversion kit and add your own motor and high end battery and ESC.

Lohring Miller
 
I have some concept drawings that I have on file that I will post on here for you guys to think about. The three big issues you will face trying to bring a new outboard product to market using a car engine will be keeping a LOW C/G, LOW overall weight and LOW customer cost. Your finished product will need to be designed to accomplish all these three of these things to have a chance of becoming the new standard outboard.

The counter rotating engine has been the culprit of 90% of the manufacturer based outboard problems from day one because you must use their custom powerhead on their lower unit. Getting away from these custom made powerheads will serve everyone well once a properly designed lower unit is manufactured that satisfies the three "Lows" mentioned.

I am retired now and have no intentions of getting a project of this size going but there are young guys out there who have the fire and machine resources to do it. Hopefully someone will take this challenge up and run with it. Once a properly designed lower unit is available that utilizes a standard car/buggy engine, your 3.5cc powerhead selection will be tremendous.

- Simply flipping a car engine over and mounting it on any of the available lower units is not an option because of the C/G issue.
 

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