Standoff-Extension Boxes, Pros and Cons

[Ratickle]

Well, Ryan is talking about putting extension boxes on his Black Thunder, http://www.seriousoffshore.com/forums/black-thunder/21393-scx-4-black-thunder-46ec-750hp-ryan9154-2.html, and I've always wondered about the pros and cons of different boxes. There are several out there, and I am starting this thread to get some feedback on them. It is something I've considerd on the Marlin, but even with the minus 2 Imco Shortie, I'm still a tad deep. So, any box on there would also have to be one of the ones that raise the height.

Here are some of what I know is available...

[Ratickle]

The ITS box from Mercruiser has a 5" setback I believe and no height change. It is the box that Doc runs on his Fountain SVL I believe. It comes with all internal steering I think, and I've been told has even less play than full external hydraulic steering.

74423

[Ratickle]

There is a Mayfair 12" setback box. I don't know much about it at all.

74424

[Ratickle]

There is a Latham 12" setback box.

74425

[Ratickle]

There is also a 7" setback box from Latham.

74426

[Ratickle]

IMCO Makes a 12" setback box. Which I believe is currently the most popular. Especially among the SVL guys.

74427

[Ratickle]

And then there is the Stelling 12" setback box that is fully adjustable and actually has u-joints and a carrier bearing from what I recall so it can be adjusted up and down.

74428

[Ratickle]

So, what do you know about setback/extension boxes. How the heck do you decide what to try? And how the heck do you even decide when to try it?

Which option is better?

12", 7", 5", nothing? If there are all of those different lengths available, why does no one make a 8", 9", or 10" box?

If you have a 20 foot boat do you use a 12" and if you have a 45 foot boat 12" is overkill and you should use a 7"? Or is the rule of thumb just the opposite? Longer boat, longer box because the water has been discomboobalated more at the stern so the drive should be farther back to find cleaner water?

????????

[TYPHOON]

This should be a good one. All I have heard was therory's and no real test data. There are several issues to talk about. Top end speed,turning quality's and getting on plane. Fountain may be the only company that might have done these test back in the day. If there ever was a time it would have been in the factory racing days but box's were not aloud with the exception of only a handfull of boats. The cost to test them would be insane unless you were a manufacture of the boat or the parts and at that every boat has a differant bottom,weight and motor. Heck, now Im even more cofused. Im with Paul anyone out there????
MD

[torrent]

The Mercury ITS is a 7 inch set back. The stelling is no longer available which IMO is a bummer since it seems to be the easiest to adjust with minor changes.

[MOBILEMERCMAN]

In general boxes and notched transoms do the same thing. They change the leverage point, make the boat act lighter and allow the drive to be raised. The lighter the boat acts the the faster it goes in flat. The opposite is true in the rough. The further back the drive is the more it is exposed to leverage when a boat spins and increases the likelihood of parts getting damaged. SVLs like the setback largely because it is relatively long for a single engine and the increased setback lightens the boat. Most SVls like all the weight as far back as you can get it. Since there are few races in rough water that is been the trend.

I think it is hard to find real info as far as what is best for an individual boat. There is so many variables acting out at once. Prop, tabs locations, operators, different CG's, and personal preferences. To get a real test the boat needs to be tested at its limit and I believe few actually operate their boats at the boats limits. Most often it is operated at the riding crews limits. When the tests performed are based on an individuals operating limits the true test of the set up change can not be evaluated.

With the past F2 boats only straight bottom boats were allowed to run boxes so long as the engine centers remained the same. Just like you can adjust them up and down you can also adjust them in. That had a positive effect on most twin engine boats. Not sure how the rules applied to F1.

Even consecutive boats in production with ever intention of being identical could be different and benefit from different set's. Partly because of crews operating preferences and in part because it is so hard to exactly duplicate a boat in every measure.

Test test test each and every boat is the only way to know for sure. It is pain staking. Every change needs every variable tested again. Few have persistence and time to test to that extreme and fewer have the means. It is so much easier to copy. Then the funny part to me is after you go through all the effort and expense to change something the natural human tendency is for many to justify their decision and say it is better. So it is hard to really know for sure when talking to people.

The easiest thing to do is just add power and run some tab like training wheels to increase your speed.

I am sure there will be many different opinions on this topic.

[MOBILEMERCMAN]

Paul, on your Marlin the best approach would be to raise the engine and use the parts you have. If your starting point is too low all the subsequent changes you are trying to make will be compromised. If you go back and up from a too low setting you are still too low.

[ryan9154]

I'm putting boxes on due to cavatation signs on props want to get props in cleaner water also good rule of thumb for every 12" back you can go up 1-2" so in my case getting the surface drive to surface more and use less trim a at wot

[Ratickle]

I know it's true they increase leverage. But I also thought the extension boxes were primarily developed to replace/make-up-for, the notched transom developement in boats. So my theory was a notched transom boat wouldn't need an extension box. I'm just really curious. If extension boxes made a 5 to 7 mph improvement, and you weren't drivng a race boat where fast cornering mattered, why wouldn't every manufacturer provide them that way?

[MOBILEMERCMAN]

good rule of thumb for every 12" back you can go up 1-2"

The water rises as it leaves the transom. When you go back 12 and up 1or 2 [ depending on the speed and a few other variables] the water actually hits the gearcase in the same place. If an increase of speed is realized it is from the balance and leverage change. Not so much from the more surfacing effect. To benefit from a more surfacing effect it needs to be raised more. That is provided you have the power and the boat is in a speed range for its size to benefit from a surfacing set up.

The handling will change for sure but the speed may or may not increase in every case. The boats that will benefit the most are the ones that run heavy in the water and respond little to trim. If the boat is already light and responsive to trim the change could be less desirable.

To Pauls point. Once a boat is molded its is what it is. How many manufactures actually go back and change the molds? Some of the high end boats improve their molds over time. Notches come in many different sizes. Plus a boat that is going to run at say 80 mph will likely enjoy a different set back then a boat running 100. Most boats are available with a range of engine options.

There are times when no matter what you do the boat runs the same speed. Different drives, ratio's heights ect make no difference. Maybe it does go faster but is twitchy and hard to control. Have you made an improvement or not. All depends on the individual. A race boat that is fast but, hard to control wins few races.

Ever wonder why the Fountains always have sand marks and touch up spots on their race bottoms? It is because even the slightest low spot has a huge effect on high speed boats. Point is the bottom is most often over looked when people are trying to make their boat go faster. Any short coming in the bottom integrity, surface or design has a huge effect on how fast it will go. In such cases changes to the set up may not change anything the speedometer does.

Say your designing a boat to race a particular class. The length limit is 30 feet. You know you want the bottom to be as long as it can be. You know the boat will appreciate a lot of set back but, you are working with a length limit. The extension box is not measured in boat length.

Possibilities and preferences are countless. My opinion is if the boat likes set back it is a better boat if it is built in to the hull. If the drives are in the basement too low re cut the transom and raise the engines.

It is hard to stay on point I will stop now.

[torrent]

I know it's true they increase leverage. But I also thought the extension boxes were primarily developed to replace/make-up-for, the notched transom developement in boats. So my theory was a notched transom boat wouldn't need an extension box. I'm just really curious. If extension boxes made a 5 to 7 mph improvement, and you weren't drivng a race boat where fast cornering mattered, why wouldn't every manufacturer provide them that way?

This is a really interesting thread and I too am just really curious. To your point most manufacturers that rig a boat with over 700hp (which in Ryans case that’s where we are currently) use #6/NXT drive which incorporate a set back into the transom assembly. Is this by dumb luck Mercury Racing decided to do this, probably not? I wonder if the #6 had no set back what type of effect there would be.

[MOBILEMERCMAN]

Ryan,
Have you tried different drive heights already? Are you looking to make it ride different or just searching for speed?

[MOBILEMERCMAN]

I am curious Ryan how did you arrive at the point you are now. Was the boat set up at the factory the way it is? Did it get re powered and or new drives hung on the back? If that is the case what was the boat cut out for originally? How fast did it go and how fast is it now?

To another point. If a boat is running well, handling well, and already going pretty fast incremental changes can make a recognizable change. For example changing heights 2"s or set back 12"s are big changes. Those changes may require a propeller change to realize the full effect. There are also times where lowering a 1/2" is in order. We have read where some new boats are set up for top speed from the factory and owners eventually enjoy a lower height. It could be from the way the boat gets loaded with gear, where its used, individual cruise speed preference, or a matter of feel.

[Ratickle]

This reminds me of Brooks's Outerlimits, the one that Dr Pete has now. That boat ended up with the 12" extensions, regular Bravo drive length, and a 1" spacer to run the props even deeper. When he got over 110 or, the boat acted weird and this setup corrected all of that from what I understand. I'll try to get ahold of Brooks and see if I recall that correctly.

[offshoreexcursion]

All I know is my Baja LOVES the Stellings boxes on the back! It feels so "dialed in" I am scared to change it. The boat handles on rails, eats up the rough, and runs around 100mph, all in a frickin BAJA! :hurray: Helping those boxes out are IMCO SC drives and 380 K Planes.

My previous 33 outlaw had 454s, bravo drives, NO boxes, 280 k planes. Nice running boat but felt like a normal boat.

My current 33 outlaw feels like A MILLION DOLLARS.

I don't know what boxes do but I truely believe in them. Whatever they are doing, it works on my boat.

[ryan9154]

Here we go the boat started out as a 575sci with xr's did mods to motor made 742 hp changed to scx-4 done a bunch of testing spinning in out,different rake props,pitch etc. Boat ran the fastest spinning in but bow steere, had to add a 1 in spacer got handling back and lost mph ran like that all season around 65 hrs had torrent (jason) hang off the back of boat when running and the water around the drives and props is full of air if I put boxes on get drives in cleaner water should be able to dial in slip easier.When you get over 700 hp slip is a big factor that people forget about.I got my rpm I can dial in with pitch but now time for slip witch if I can get that dialed in the boat should all around be better.We have tried everything with the props and slip is still high.I'm not going to get into all the tech on props but jeff at hering and brett at bblades are doing all the prop work together.Got thousands into shipping and trying different props.

[MOBILEMERCMAN]

It seems to me your are on the right track with boxes. IMCO makes good stuff. Since you have found the height threshold on the boat you are half way there. It is great you have all the adjust-ability the IMCO drive has to offer. I agree back and up as you said 12 plus 1. The change in attitude will probably allow you to go up second inch[ the one you spaced down for] and not bow steer. No telling until you try it it might even tolerate 1/2 or 1 more to boot.

I suspect that change will make the boat feel more nimble and more fun to run. As big as the boat is the extend reach of the props back will prove helpful in the rougher stuff too.

Perfect time to get started and be ready for next season.

[Ratickle]

Ryan, how much did it slow down when you added the spacer? From what to what?

And have you checked the bottom really close for any imperfections yet? Jim can explain the differences in small hoks and imperfections better than I can. And how they make bigger differences at the faster speeds.....

[ryan9154]

Spacers only slowed down 2 to 3 mph.And the bottom is pretty close not blueprinted but close.I've done some much testing and it's consistent if the bottom was really off the testing wouldn't be consistent.

[Ratickle]

So you've checked all the little stuff? No hooks, rocker, pits, bumps etc? Sometime when you're in this area give me a shout. You would not believe some of the stuff on the bottom of mine.....

[Ratickle]

Of course, now you've made another question come to mind. When you blueprint a bottom, because of a step boat do you also have to blueprint the area of the two steps to each other?

[MOBILEMERCMAN]

The important thing is to make sure there are no low spots in any of the main running surfaces. A low spot or hook causes a vacuum and has a huge effect on speed. The effects increase the faster you go. Sharp tailing edges and stakes are less important at 80 then at 100 and up. A significant low spot in a critical area can create a level drag that is so great at speed that it will make any change in props , heights or set up seem irrelevant.

[Tinkerer]

What is considered significant?

[MOBILEMERCMAN]

It changes based on what the boat is running speed wise. I am not aware of any chart or hard fast rule but, in general based on what I have witnessed say more than 1/4 on a 70 mph, 1/8 at 80, A 1/16 at 90, and any light seen under a straight edge at a 100 or more on the running surface or surfaces. The size of the low spot will factor in as well.

[Tinkerer]

WOW

[Tinkerer]

What do you use to fill these low spots?

I hung my old Glastron from My garage ceiling years ago and blueprinted the bottom. I made everything smooth and straight.
That boat worked when I got done with it. Wish I still had it today. I would put adifferent drive on it so that it wouldn't blow every other weekend. Over 500 HP SBF.

[Ratickle]

Do you recall the comparison of before and after? And how much work/changes you had to do?

[Tinkerer]

It was sitting on a roller trailer for the first 7 years I owned it and at every roller the bottom was indented. Converted the trailer to a bunk and smoothed the bottom and regelled it. Way too many years ago to remember how much work it was, I had a bad habit of making MAJOR changes so I couldn't tell you what improvement that created. It helped with handling - that and raising the drive so the shaft was 3 inches below the pad. That boat flat out flew when I got done with it. It was one ill handling boat with HP added when it was stock. Stock it did 50 MPH with 188 HP. best I saw was 94 GPS before I sold it.

[Tinkerer]

Thinking on buying two IMCO neutral boxes, hyd rams and hardware, inner transom mounts. Basicly everything to add boxes and hyd steering to my boat except the helm and hoses. $6400 plus shipping --- what do you think??

[ryan9154]

New boxes with everything but the steering rams are around $5700 thats the hd shafts boxes inner plates hardware and wing plates.That was a quote I got for 2 of everything.

[Ratickle]

Is that $5700 each when puchasing two?

[ryan9154]

It was 2850 each when buying two that was my quote not sure if I got a deal have spent alot of money with imco in the last year. So 5700 total for two setups.

[Ratickle]

That seems like a decent price to me. If course that doesn't invclude the power steering pieces like he was asking about above. They both seem like decent deals to me.

[Ratickle]

Did you make any decision on the stagger yet Ryan?

[ryan9154]

Think keeping jason's GT side by side they just had their baby boy so he'll be busy for a bit.

[Ratickle]

Think keeping jason's GT side by side they just had their baby boy so he'll be busy for a bit.

I think that's the right thing to do anyway. I know the stagger helps some, but with the other technology, I don't think its worth the major work required (unless you're racing it).

But, if he still decides to do it, there will sure be a lot of attention paid to the project......

[TUCK646]

Pros buy them,
Cons steal them,
either way mine always worked .

[Ratickle]

Do you have any before and after results?