RDP’s new float for 2024!

[DarkHorseRacing]

How do those exhaust tips work?

 

[Big B Hova]

Daves been busy with gelcoat murals already

 

[RiverDave]

Daves been busy with gelcoat murals already View attachment 1387178

This! Lmao!

 

[RiverDave]

How do those exhaust tips work?

They are spring loaded mufflers.. when the engines fire they come out a little when you add throttle they come out more..

I’d like to get rid of them but they are through bolted so I gotta get new tips..

 

[RiverDave]

So our first round of prop tests

Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.

4000 rpm - 64 mph

Wide open slightly over trimmed 5,000 rpm 78 mph.

The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34

I’m wondering if the scx lowers are really scrubbing that much speed off this thing.

For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..

 

[mash on it]

@RiverDave , you need to use a radar gun.

Great looking float too.

Dan'l

 

[DarkHorseRacing]

View attachment 1387187 View attachment 1387188 So our first round of prop tests

Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.

4000 rpm - 64 mph

Wide open slightly over trimmed 5,000 rpm 78 mph.

The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34

I’m wondering if the scx lowers are really scrubbing that much speed off this thing.

For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..

So you need 30’s or 32’s?

What’s Chad running for props? Are his turning out like yours? Lots of variables, including the weather.

 

[RiverDave]

@RiverDave , you need to use a radar gun.

Great looking float too.

Dan'l

I’d rather use my phone gps.. right now I went out by myself and it’s hard to hold the phone take the screen shot / take the picture etc..

I’m battling a couple problems on the gauges as well. The left tach has a ground problem so it’s all over the place.. and the gps keeps dropping to zero, then 30, then back to reading right..

Absolute speed and marine is going to be on that and a water pump problem next week.

RD

 

[RiverDave]

So you need 30’s or 32’s?

What’s Chad running for props? Are his turning out like yours? Lots of variables, including the weather.

The motor I believe redlines at 6000, or 6200? So if anything I’d have to goto 26’s.. but something isn’t right here.


I just called Scott at Ilmor and he more than likely built these engines and set the boat up originally.. so he’s going back to check his notes and talk to the engineering side and get back with me tomorrow.

RD

 

[RiverDave]

So with the prop slip calculator we are currently running a 12% slip.

 

[Blackmagic94]

View attachment 1387187 View attachment 1387188 So our first round of prop tests

Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.

4000 rpm - 64 mph

Wide open slightly over trimmed 5,000 rpm 78 mph.

The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34

I’m wondering if the scx lowers are really scrubbing that much speed off this thing.

For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..

12% slip not bad but you might be able to get it down to 10-11 at best on big vee

 

[throttle]

Do with the prop slip calculator we are currently running a 12% slip.

that's better. and its warming up so you still loosing some rpm

 

[RiverDave]

So in theory if I put on 26’s and run it to the rev limiter of 6200 (actual is 6300) the boat should run 90.

I’d be fine with that and keep the larger scx lowers.. if it doesn’t do that we will likely switch to sc lowers to pick up the extra 10mph.

RD

 

[Big B Hova]

So "have you tried a different prop?" actually applies to this thread.

 

[RiverDave]

So "have you tried a different prop?" actually applies to this thread.

Oh we are gonna try quite a few different props.. lol

RD

 

[chadzilla]

So you need 30’s or 32’s?

What’s Chad running for props? Are his turning out like yours? Lots of variables, including the weather.

I had a set of bravo 32" that were hacked n wacked so who knows what they actually were. Ours cavitated pretty good coming on plane with those but, I was able to get up on a single ski with them so... I have tried a set of 30" Maximus props but could only spin them to 5000 rpm or so at around 81. They had very little cavitation coming on plane. I have a set of bravo 30" on there now. Again, very little cavitation coming on to plane. I haven't run them wot yet though. Mine are turning out as well. Our boat is a much different set up though. It has Imco SCT uppers with SC lowers, stand-off boxes and transmissions. I have personally seen a tick over 90mph up here. We are at 1800" of elevation too. The gps has seen 94 and I believe it.

 

[RiverDave]

I’d be curious as to what frogman’s x dimension is, and specs etc.

 

[Bucketlist]

Dave, congratulations to you and family! Very nice looking boat. You need to name this boat “Make Boating Great Again” That is my favorite RDP T shirt.
Also, check if there is adequate airflow to these engines. Your pictures don‘t show a lot vents. Maybe this is one of several issues contributing to performance that you refer too.

 

[FROGMAN524]

So in theory if I put on 26’s and run it to the rev limiter of 6200 (actual is 6300) the boat should run 90.

I’d be fine with that and keep the larger scx lowers.. if it doesn’t do that we will likely switch to sc lowers to pick up the extra 10mph.

RD

I’ve run my boat with 32 pitch Maximus props and 1.5 gears to 103MPH at 5,500RPM. FYI.

 

[RiverDave]

Dave, congratulations to you and family! Very nice looking boat. You need to name this boat “Make Boating Great Again” That is my favorite RDP T shirt.
Also, check if there is adequate airflow to these engines. Your pictures don‘t show a lot vents. Maybe this is one of several issues contributing to performance that you refer too.

There’s plenty of vents.. there’s four large ones on each side of the funnel, and then there are vents all across the top at the top of the swim
Step area.

 

[Runs2rch]

I’ve run my boat with 32 pitch Maximus props and 1.5 gears to 103MPH at 5,500RPM. FYI.

That shows the power the SCX drives scrub compared to XR's. Boat ran that with the motors in stock form at 5200.

 

[Runs2rch]

So in theory if I put on 26’s and run it to the rev limiter of 6200 (actual is 6300) the boat should run 90.

I’d be fine with that and keep the larger scx lowers.. if it doesn’t do that we will likely switch to sc lowers to pick up the extra 10mph.

RD

So when we looked at this boat for sale in 2016 it had 24 Bravo 1's. Had a pair of 26's in the boat. Owner used the boat at Powell mainly. Makes sense now. I forgot the rev limiter was that high.

 

[FROGMAN524]

That shows the power the SCX drives scrub compared to XR's. Boat ran that with the motors in stock form at 5200.

On Lake Tahoe 2 years ago, with 5 people in the boat and a half tank, and these props, best I got was 93. Don’t remember the RPM.

 

[Runs2rch]

On Lake Tahoe 2 years ago, with 5 people in the boat and a half tank, and these props, best I got was 93. Don’t remember the RPM.

That is great on Tahoe.

 

[Not So Fast]

Nicely kept Dave, the way an older boat should look
NSF

 

[Blackmagic94]

I think the problem right now is it’s just not letting it roll over to higher rpm and thus more hp will which net more rpm and more hp and then more rpm


I’m thinking 26s are gonna help a lot only if they are labbed

 

[ToMorrow44]

View attachment 1387187 View attachment 1387188 So our first round of prop tests

Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.

4000 rpm - 64 mph

Wide open slightly over trimmed 5,000 rpm 78 mph.

The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34

I’m wondering if the scx lowers are really scrubbing that much speed off this thing.

For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..

I think you have 1.35 ratio drives. The numbers don’t make sense with 1.50. Max RPM I think is 6400 on the Ilmors.

Do you have the original SCX lowers with the blunt nose?

 

[RiverDave]

So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..

That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..

I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?

So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..

I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.

Motors have been gone through so there is no issues there to my knowledge.

So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.

If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..

 

[Sharp Shooter]

That's a great lookiin battle ship! Really like the trailer wheels!

 

[mbrown2]

Great troubleshooting...

 

[JFMFG]

If you dropped it off how are you gonna be at the run Saturday? jk

 

[OldSchoolBoats]

Boats going to be loud AF now too....lol. Great troubleshooting

 

[DarkHorseRacing]

So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..

That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..

I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?

So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..

I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.

Motors have been gone through so there is no issues there to my knowledge.

So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.

If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..

View attachment 1411087 View attachment 1411088 View attachment 1411089 View attachment 1411090 View attachment 1411091

Is turning the props to the outside the ideal setup in your case?

 

[28Eliminator]

If they’re both turning the same RPM, I’m not sure how that makes sense???

Have you tried giving it more Stbd throttle to see if the boat straightens up?

 

[chadzilla]

So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..

That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..

I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?

So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..

I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.

Motors have been gone through so there is no issues there to my knowledge.

So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.

If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..

View attachment 1411087 View attachment 1411088 View attachment 1411089 View attachment 1411090 View attachment 1411091

Hopefully that is the case Dave! I would think you would have seen that on the tachs though. Glad you are ditching those crappy mufflers. I love CMI but those mufflers are the worst. We have the IMCO gatlins on ours and I really like how they sound. Not too loud but loud enough!

 

[outboard_256]

If they’re both turning the same RPM, I’m not sure how that makes sense???

Have you tried giving it more Stbd throttle to see if the boat straightens up?

You can have an engines turning an RPM and have different loads on it. One engine could be producing the power and the other "coasting" and creating drag.

 

[69hondo]

Loud pipes save lives.
The way it should be

 

[Bigbore500r]

You can have an engines turning an RPM and have different loads on it. One engine could be producing the power and the other "coasting" and creating drag.

This is an excellent point

 

[28Eliminator]

You can have an engines turning an RPM and have different loads on it. One engine could be producing the power and the other "coasting" and creating drag.

The coasting prop is going to be be turning slower... there's no way around that. Prop slip says its impossible for the coasting prop to be turning the same RPM as the one producing the power.. it might be close...

Still, If more power (even more RPM) is added to the stbd engine, will the boat straighten up?

IDK.. Lol... I've never owned a twin engine Boat.

 

[outboard_256]

The coasting prop is going to be be turning slower... there's no way around that. Prop slip says its impossible for the coasting prop to be turning the same RPM as the one producing the power.. it might be close...

Still, If more power (even more RPM) is added to the stbd engine, will the boat straighten up?

IDK.. Lol... I've never owned a twin engine Boat.

Ok how about I say it like this. Let's say one engine for what ever reason isn't running 100%. Doesn't gain power after 4000 rpm like it should. The other engine runs normally. When you get to 5800 rpm engine number 1 is turning that rpm but only producing 650 HP. The 2nd engine at the same rpm is producing 700 hp. This would cause the boat to pull to one side. It will turn to what ever side has less HP.

To answer your 2nd question. If you were to add power or rpm to the stbd engine to match the other side it would drive straight.

If RD could mount go-pro's filming the exhaust as he goes high rpm you could probably see which exhaust isn't opening fully and confirm his theory.

 

[JFMFG]

Loud pipes save lives.
The way it should be

Biggest struggle I have since switching to outboards I miss that big block sound.

 

[69hondo]

Biggest struggle I have since switching to outboards I miss that big block sound.

Outboards sound decent but nothing beats the sound of a healthy big block

 

[Motoxxxloak]

I’d rather use my phone gps.. right now I went out by myself and it’s hard to hold the phone take the screen shot / take the picture etc..

I’m battling a couple problems on the gauges as well. The left tach has a ground problem so it’s all over the place.. and the gps keeps dropping to zero, then 30, then back to reading right..

Absolute speed and marine is going to be on that and a water pump problem next week.

RD

Would like to know if the tech is just a ground issue? Mine has done the same since I bought it and I’ve never had the mind to start poking around

 

[ToMorrow44]

So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..

That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..

I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?

So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..

I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.

Motors have been gone through so there is no issues there to my knowledge.

So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.

If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..

View attachment 1411087 View attachment 1411088 View attachment 1411089 View attachment 1411090 View attachment 1411091

I bet if you swapped out those lowers for DDS lowers you’d pick up 10mph.

 

[Runs2rch]

Boats going to be loud AF now too....lol. Great troubleshooting

This. Dave is probably going to go tips, then clamp on's if he doesn't like the sound.

 

[poncho]

Nice boat Dave, I enjoy these troubleshooting threads, one can always learn.

 

[4Waters]

So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..

That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..

I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?

So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..

I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.

Motors have been gone through so there is no issues there to my knowledge.

So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.

If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..

View attachment 1411087 View attachment 1411088 View attachment 1411089 View attachment 1411090 View attachment 1411091

Just the tips

 

[RiverDave]

If you dropped it off how are you gonna be at the run Saturday? jk

They asked me if I wanted it done for the weekend. lol.

That said we decided to stay home

 

[RiverDave]

Ok how about I say it like this. Let's say one engine for what ever reason isn't running 100%. Doesn't gain power after 4000 rpm like it should. The other engine runs normally. When you get to 5800 rpm engine number 1 is turning that rpm but only producing 650 HP. The 2nd engine at the same rpm is producing 700 hp. This would cause the boat to pull to one side. It will turn to what ever side has less HP.

To answer your 2nd question. If you were to add power or rpm to the stbd engine to match the other side it would drive straight.

If RD could mount go-pro's filming the exhaust as he goes high rpm you could probably see which exhaust isn't opening fully and confirm his theory.

I didn’t have a GoPro with me but we put a drone up and then flew a couple feet off the water and up to the back of the boat to try and get a look but there’s so much water / mist flying around it’s hard to see..

So we just ditch the mufflers.. I wanted em gone anyways and the likelyhood that it’s causing the issue is pretty high.

We haven’t dived into the tach and speedo issues yet but that’s next.. I’ll freely admit it would make life a lot easier for trouble shooting with two tachs.. but this is so obvious it is pretty easy to feel.

RD

 

[RiverDave]

The coasting prop is going to be be turning slower... there's no way around that. Prop slip says its impossible for the coasting prop to be turning the same RPM as the one producing the power.. it might be close...

Still, If more power (even more RPM) is added to the stbd engine, will the boat straighten up?

IDK.. Lol... I've never owned a twin engine Boat.

It probably is turning slightly slower, but it’s still making power so it wouldn’t be by much.. I dunno without two tachs ya can’t tell. lol. The power being delivered in the port side though is creating more lift.