Question with my my factory lower unit.

[headgames]

Im a new member to this site and this is the first time i've posted....i have a factory merc lower unit on my carbed 2.4,it has a bobs nose cone,bobs cavitation plate and low water pick-up...my question is how fast can i safely run this set up with the stock gear case,it has never been repaired or welded.Thanks

[petehubbell]

Welcome to Scream and fly! Tell us some more about your boat and how it's set up. ( Hull, Prop, Set back, Motor height) Lots of knowledge on this site.

PH

[headgames]

My boat is an 18 ft laser mod v-tunnel,it has a manual jack plate that is set back approx. 8 in.,it has a 26p prop on it.This is my first go fast outboard boat however i have owned many v-drives and jets...i am currently rigging this boat and never actually put it in the water yet...Thanks for yr help.

[petehubbell]

Laser=T-Rex! Your in luck. There are plenty of guys on here with Laser knowledge. I'm not one of them but T-Rex or DaBull might chime in they'll know whatcha need start with. If you haven't already done so, take pictures of your boat/motor.

PH

[gary slagle]

welcome to the fun, good to see you today ,bout time you joined s & f ! waay better than tv .i wouldnt think that you will run into problems with your lu,but it'd always good to be concerned when it comes to safety.i'm sure some of the experts here will give advice.

[headgames]

Thank's Gary...We had a great time yesterday hangin with u guys!Yr right...I should have joined this forum along time ago,lots of knowledge on here that will help me with my new project.

[transomstand]

Im a new member to this site and this is the first time i've posted....i have a factory merc lower unit on my carbed 2.4,it has a bobs nose cone,bobs cavitation plate and low water pick-up...my question is how fast can i safely run this set up with the stock gear case,it has never been repaired or welded.Thanks

As long as the case is in good condition, it will present no safety issues. It will run as fast as the power will take it.

[delgrad59]

I really like this question also. Is there a strength difference between preloaded shafts and non preloaded shafts? Also I have heard that there are big gear cases and smaller gear cases is this true? Something about cases after 1647-9147C1? Dont want to hijack a thread but I have a similar question in that when you get to larger hp motors is there a chance of a major malfunction with a stock case that will cause the gears/shafts/etc to fracture and cause the motor to rev into no mans land? And if this happens and you immediately lose thrust what happens to the boat? I had my old inline shut off on my hydrostream at 60 and cannot imagine losing thrust at 80 or 90. Hope to see you out there headgames.

[transomstand]

I really like this question also. Is there a strength difference between preloaded shafts and non preloaded shafts? Also I have heard that there are big gear cases and smaller gear cases is this true? Something about cases after 1647-9147C1? Dont want to hijack a thread but I have a similar question in that when you get to larger hp motors is there a chance of a major malfunction with a stock case that will cause the gears/shafts/etc to fracture and cause the motor to rev into no mans land? And if this happens and you immediately lose thrust what happens to the boat? I had my old inline shut off on my hydrostream at 60 and cannot imagine losing thrust at 80 or 90. Hope to see you out there headgames.

Pretty much, that's all true. Gearcase selection will be based on application, and individual preference. ANY gearcase can fail at speed, the results can be anywhere from benign, to catastophic, each situation is unique.

[Sonik]

A healthy (inside and out) Bobs coned 200 case will more than likely run as fast as you want to go in that boat. But this is a function of propshaft height and trim angle as well. Generally, the higher the propshaft height, the less the water must path around the case....additionally, trim angle plays a big part as cases don't track through the water clean when you introduce alot of positive trim and will blow out at a much lower speed. Depending on application and propshaft height, your prop will most likely lose bite before you actually blow the case out when adding excessive amounts of positive trim....which, for your hull, shouldn't really be an issue at all.

Delgrad - the XR4 and XR6 gearcases have a smaller bullet diameter than the 200 cases and are the hot ticket for drag racers. Smaller bullet travelling through the water = less hydrodynamic drag = more speed. But, the stock guts on these cases are somewhat inferior due to size limitations within the case to include a less beefy skeg....and we know how important the skeg is when running ridiculously high propshaft heights. (I'm sure I'll start an argument with that one)

Now, as far as your question about catastrophic failure, I agree with Pete...they all can fail, given the proper circumstances and/or abuse/lack of maintenance. I had a pinion failure this year.....was on the gas and accelerating hard and the pinion grenaded at about 70mph turning around 6K rpm. Pinion pieces caused the case to bind, which split the case, broke the screws I had installed to hold the carrier from spinning, snapped the webbing on the carrier and twisted the driveshaft off in the powerhead. The boat nosed over and rolled 20 or so degrees to port and the motor hit 8K before I realized what happened and could lift. Fortunately I was still trimming and didn't have it strung out because the outcome could have been very different. Noone was hurt (other than my pride by having to be towed in by a couple really nice fisherman), we all wear safety gear and kill switches every time in the boat. You can ask the guys that know me, I'm very particular about my stuff and am on top of preventative maintenance....but s%*t still happens.

I also agree....Rex and Bull are your guys on the Laser no doubt. Good luck and welcome to the boards!

[headgames]

Thanks so much guys...that is very useful information.The gearbox is in the shop now getting pressure tested and fresh gear oil,i'll run it for now and i'm sure i'll have more questions in the future...Thanks again!!