Water Pickup... at 90+ mph

Randell Doane · Jul 23, 2017

Hello,

I'm trying to set the record in B class outboard hydro, and I had a question with regards to the water pickup. At 90+ mph (which is what I am hoping to achieve) will this prop have time to fling water up into the pickup? The LU is a Lawless 3.5 and the pickup from hyperformance. The original lawless pickup is much larger.

Thanks in advance!

Mark Poole ModVP · Jul 23, 2017

Just a suggestion, you might want to consider locking the engine and using a rudder. (Allowed in O/B hydro) This solves two problems. Far less strain on the steering servo, which would be a lot at that speed. It also allows you to take the cooling water from the rudder which means no flow issues. I would also think that at 90 mph, eliminating the skeg's 'slip stream' from in front of the prop helps too.

Randell Doane · Jul 23, 2017

Unfortunately I already have it built so I'd like to keep it as is. I see what you are saying about the slip stream, but fortunately the skeg on the Lawless is very hydrodynamic. If I were to keep it as is, would you think there is a risk of it not getting water?

Carl Van Houten · Jul 23, 2017

Randell Doane said:
Hello,

I'm trying to set the record in B class outboard hydro, and I had a question with regards to the water pickup. At 90+ mph (which is what I am hoping to achieve) will this prop have time to fling water up into the pickup? The LU is a Lawless 3.5 and the pickup from hyperformance. The original lawless pickup is much larger.

Thanks in advance!

I that it that this is a custom built boat. Post a picture of what you have now.

Glenn Quarles · Jul 23, 2017

Do you think you will need water cooling at all?

GQ

Randell Doane · Jul 24, 2017

Here are some pics. I don't technically need water cooling, but by restricting water flow I can get the engine temperature to exactly where I want it much more easily which should help increase rpms at WOT

Randell Doane · Jul 24, 2017

I just realized this didn't attach in the initial post, but here is the LU and water pickup

Jerry Dunlap · Jul 24, 2017

Anyone know the best speed achieved by a JAE 21 and an inboard 21?

I just did some checking and Martin Truex, Jr holds both the NAMBA and IMPBA 20 Hydro 1/16 straightaway at 110 mph or so. The hull is a "Truex" which I would imagine is pretty similar in some ways to a JAE 21.

JD

Carl Van Houten · Jul 24, 2017

Randell Doane said:
I just realized this didn't attach in the initial post, but here is the LU and water pickup

If I were trying to get anywhere near the speeds you are hoping for, I would put that stock skeg on a serious diet. Cut about 1/4 to 5/16 inch off of the over all length of your skeg and I would also cut the trailing edge at least 1/4" forward. After you get that done, you should sit down with a good sharp double-cut file and get ready to spend about an hour or more thinning that skeg until it is somewhere close to .093" at its thickest point. Be careful doing this because if you taper it more on one side than the other it will be jacked up and can cause some handling issues. While thinning it I would occasionally stop and look straight down on the skeg (from the bottom end) to see that you are maintaining an equal shape on each side of the skeg. I finish sand mine using 320 grit paper.

I see you have modified the cav-plate so you could hang some serious prop on it also. Just looking at the picture, I would also mention that the prop looks fairly dull across its leading edge. Work the back side of the blade and get that prop thin and sharp. Good luck.

Keep us posted on your progress.

-Carl

LohringMiller · Jul 24, 2017

Mike Bontoft set the NAMBA outboard hydro record at 81+ mph that still stands. Its engine was air cooled. The difference with outboards is that the CG is way back. The traditional way to deal with this is with rear sponsons. Full size outboard hydros actually plane on their transoms with the sponsons out of the water. Mike's model solution was with a wing. His full size outboard hydro holds the world record for electric boats at 98+ mph. It flies with the transom mostly out of the water at over 85 with a notable drop in the power required. By the way, we deliberately lifted the water pickup out of the water on our record gas hydros. It only was used to cool the engine while the boat idled during the turn around. I doubt that you need cooling during the short SAW run if at all.

Lohring Miller

Carl Van Houten · Jul 24, 2017

LohringMiller said:
Mike Bontoft set the NAMBA outboard hydro record at 81+ mph that still stands. Its engine was air cooled. The difference with outboards is that the CG is way back. The traditional way to deal with this is with rear sponsons. Full size outboard hydros actually plane on their transoms with the sponsons out of the water. Mike's model solution was with a wing. His full size outboard hydro holds the world record for electric boats at 98+ mph. It flies with the transom mostly out of the water at over 85 with a notable drop in the power required. By the way, we deliberately lifted the water pickup out of the water on our record gas hydros. It only was used to cool the engine while the boat idled during the turn around. I doubt that you need cooling during the short SAW run if at all.

Lohring Miller

OB hydro.JPG

P1010007.JPG

IMG_4004.jpg

I agree with Lohring and Glenn you will need some heat to get a hit with that prop. I held that record for a few years and I did it with the skeg removed and steered with a rudder as previously mentioned. Much like Mikes hydro.

Mike Hughes · Jul 24, 2017

MIike Bontofts boat is steered with the skeg. Its NAMBA record. They do not allow the use of a rudder. The outboard must steer the boat. Mike and I talked about what he needed to get it legal when he was thinking about going for the record. Its a custom built leg with an inboard motor mounted to it. The steering cables run thru the wing in a big loop and has a clamp on it as it crosses over the leg. I think at the time the record stood at 65 ish. Pretty much smashed it. I think Mike said there was more speed to be had. Lohring can chime in here. But that was a long time ago. Memory aint what it use to be. LOL

Mike

Carl Van Houten · Jul 24, 2017

Mike Hughes said:
MIike Bontofts boat is steered with the skeg. Its NAMBA record. They do not allow the use of a rudder. The outboard must steer the boat. Mike and I talked about what he needed to get it legal when he was thinking about going for the record. Its a custom built leg with an inboard motor mounted to it. The steering cables run thru the wing in a big loop and has a clamp on it as it crosses over the leg. I think at the time the record stood at 65 ish. Pretty much smashed it. I think Mike said there was more speed to be had. Lohring can chime in here. But that was a long time ago. Memory aint what it use to be. LOL

Mike

Mike, After reading your post I went back and looked and I guess I just didn't look at it close enough to see that it was just an offset skeg and not a separate rudder. I had never notice you guys had done that before. Randell, if the is anything I can help you with anything just PM me and I will do what I can to help you.

-Carl

Randell Doane · Jul 24, 2017

Wow, this has been a plethora of information for me! I didn't think about thinning the skeg, but will definitely do so. By the same token, should I consider thinning the turn fin? It is sharpened but is the heck of a lot wider than the stock skeg on the Lawless. And since I still plan to keep it water-cooled, do you think there is any risk of it not getting water during long runs? And to Carl, I really appreciate the offer, I will probably take you up on it at some point!!

Carl Van Houten · Jul 24, 2017

Randell Doane said:
Wow, this has been a plethora of information for me! I didn't think about thinning the skeg, but will definitely do so. By the same token, should I consider thinning the turn fin? It is sharpened but is the heck of a lot wider than the stock skeg on the Lawless. And since I still plan to keep it water-cooled, do you think there is any risk of it not getting water during long runs? And to Carl, I really appreciate the offer, I will probably take you up on it at some point!!

I will be glad to help but 90 mph is a tall order. That would be the fastest outboard in the books. I'm not going to say it can't be done at some point but let's just get your gear and setup cleaned up and go from there. I set my record with a mini turn fin. Just enough to turn the boat around at low speeds to get another run at the beams.

-Carl

bzubee · Jul 25, 2017

I would suggest attending a SAW recrd trial sometime in the future you will pick up all sorts of ideas and tips just go and watch.

LohringMiller · Jul 25, 2017

Mike Hughes said:
MIike Bontofts boat is steered with the skeg. Its NAMBA record. They do not allow the use of a rudder. The outboard must steer the boat. Mike and I talked about what he needed to get it legal when he was thinking about going for the record. Its a custom built leg with an inboard motor mounted to it. The steering cables run thru the wing in a big loop and has a clamp on it as it crosses over the leg. I think at the time the record stood at 65 ish. Pretty much smashed it. I think Mike said there was more speed to be had. Lohring can chime in here. But that was a long time ago. Memory aint what it use to be. LOL

Mike

The boat was probably good for close to 90 mph. At the time the NAMBA 3.5 hydro record was under 100 mph. Mike thought he might have a shot at that until Mark Grim and Steve O'Donnel had a duel that pushed the record to 107. Mark has gone even faster since.

Lohring Miller

Christian Lucas · Jul 25, 2017

Hi,

and think about a counter rotating propeller , maybee inline or side by side . With such the skeg can be very very small. For ic engine two gear with one motor is no problem like a W-drive in drag boats. So only one engine to start and run smooth .

my first self build outbord in the 70tys was only a brass tube with no skeg that worked wonderfull.

Happy Amps Christian

Carl Van Houten · Jul 25, 2017

LohringMiller said:
Mike Hughes said:

MIike Bontofts boat is steered with the skeg. Its NAMBA record. They do not allow the use of a rudder. The outboard must steer the boat. Mike and I talked about what he needed to get it legal when he was thinking about going for the record. Its a custom built leg with an inboard motor mounted to it. The steering cables run thru the wing in a big loop and has a clamp on it as it crosses over the leg. I think at the time the record stood at 65 ish. Pretty much smashed it. I think Mike said there was more speed to be had. Lohring can chime in here. But that was a long time ago. Memory aint what it use to be. LOL

Mike

Click to expand...

The boat was probably good for close to 90 mph. At the time the NAMBA 3.5 hydro record was under 100 mph. Mike thought he might have a shot at that until Mark Grim and Steve O'Donnel had a duel that pushed the record to 107. Mark has gone even faster since.

Lohring Miller

I will help him as much as possible. I think he is going to have a blast and it sounds like he has gotten bit by the"speed bug".

Randell Doane · Jul 25, 2017

Carl Van Houten said:
LohringMiller said:

Mike Hughes said:

MIike Bontofts boat is steered with the skeg. Its NAMBA record. They do not allow the use of a rudder. The outboard must steer the boat. Mike and I talked about what he needed to get it legal when he was thinking about going for the record. Its a custom built leg with an inboard motor mounted to it. The steering cables run thru the wing in a big loop and has a clamp on it as it crosses over the leg. I think at the time the record stood at 65 ish. Pretty much smashed it. I think Mike said there was more speed to be had. Lohring can chime in here. But that was a long time ago. Memory aint what it use to be. LOL

Mike

Click to expand...

The boat was probably good for close to 90 mph. At the time the NAMBA 3.5 hydro record was under 100 mph. Mike thought he might have a shot at that until Mark Grim and Steve O'Donnel had a duel that pushed the record to 107. Mark has gone even faster since.

Lohring Miller

Click to expand...

I will help him as much as possible. I think he is going to have a blast and it sounds like he has gotten bit by the"speed bug".

Haha you got that right! Leisure boats have their place too, but I really do want to push the limits of what an outboard can do!

Water Pickup... at 90+ mph

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