Raising X dimension
 

Looking for some pros and cons. I tried this on the formula section of the site, but didnt get many hits. I'd like to see better handling, cruise speed, top end out of the boat. I already am having the transom redone so it wouldn't really cost much more to raise the dimension.

I have a 93 271 with a 502 efi in it. I was wondering if anyone has raised the x dimension on their boat. Any benefits? Negatives? How much should i raise it if any at all. I called formula and talked to scott. He also wasnt sure about the effects it would have. The boat was built back when they didnt have 4 blade props available, so im wondering if i were to raise it and run a 4 blade if it would handle better/increase speed. Thanks for your help

I'm far from an expert but IMO I wouldn't modify the transom to raise the prop depth(X and prop depth are 2 different animals by the way) The easiest and cheapest way to raise or lower the prop depth is via shortie lowers and or spacers. After your transom work gets done and the boat is back together running again, I would pick up a pair of -2 lowers and try them as is and see what happens. If it's too loose then you could space back down. If it doesn't work for you at all, you can easily sell the shorties and go back. Modify the transom and your stuck with it. Every boat and hull is different and responds differently to changes, It's all trial and error so permanent changes are not the way to go IMO.

What is the original x-dim? If it's low like 6-8" I would say raise it. You can always space down. Problem with running a shorty, being it an XR or SC, the nosecone can be a negative thing, unless you run 80+ or so. If it was me, I would put the prop shaft at 5" below ie. an x-dim of 16.725"-17" and then space it down if needed.

Not 100% sure of the current x dimension, the boat is at glassdave's shop so hopefully he will chime in. I also have a call in to formula regarding the difference between my x dimension and a newer 271. Thanks for the comments, keep em coming!

Your boat may have an X for a Mirage style propeller. The Bravo 1's had higher dimensions. That's the issue I ran into with my boat.

I modified my transom, raised the drives/engines 2 inches and picked up speed all over the RPM band. My drives were 7 1/2" propshaft depth, now they're 5 1/2". I could have went even higher but I went by what the manufacturer suggested for X Dimension with a Bravo 1 prop. http://s706.photobucket.com/albums/w...view=slideshow

Dave will know what to do, I called him many times during my project for advice. If you do decide to go up, nows the time to do it because it's much cheaper than buying a lower unit IMHO>

if your transom is not notched first thing you need is an extension box then raise your drive as much as you can with shorter lowers which is -3 when you do that you will need a 6 blade hering nothing else will work as good been there done that .bow lift is what you don't want to loose with a non stepped bottom.

It is set up for a mirage prop, thats what it came with from the factory. I think you might be on to something. Did you experience any negative effects like longer planing time, or decreased handling. Thats something im really not willing to lose

I will pop the jig on it tomorrow and get the boats actual X dim. It is pretty deep though.

You should be able to set it up with the propshaft about 5" below the bottom and still get decent bow lift.
I wouldn't go any higher than that though. You need it deep enough to carry the bow.

I raised mine 4" last winter. Its now 4.5" below. The problem I ran into was the 4 blade props would blow out when turning sharply .. ie water sports. Slip also went up. The boat is faster. I swicthed over to 5 blade props to stay hooked up & that kills most of the speed advantage. I'm going to lower the drive back to 5" below & hope the slip improves.

Just put the jig on it and its at 15 and maybe a quarter, she's pretty deep (6 3/4 deep).

Anyone see the article in SportBoat this month on X dim? Great read, says for a single the optimum is for the prop to be between 4 and 5 3/4 inches below the bottom which puts the X dim at 17 3/4 and 16 respectively. When i re did my Scarab last year i put my mine at 17 3/4 and its a whole different boat. Planes better trims better rides better, mostly because now i can run a better prop.


I agree, still a good all around performance X dim without getting nuts.

I didn't get "radical" with my X Dimension so, no, I didn't have any negative effects at all.

Time to plane stayed exactly the same. The boat required less trim to get the same amount of lift. The boat was better balanced and I picked up a few mph in cruise speed and 5-6 mph on top end. If you raise the X up to where you can start running a bravo 1 (4 blade), I think your cruise speed will go up a great deal over the Mirage.

I think Dave has you on the right path, I'd just go with what he suggests!

What is the transom angle? I'd say go with 16,7/8".

Bring it up to curent std and call it a day and lose that old three blade maybe put it in the front yard next to the gnome lol they are equally scary and old.
17 5/8

Oh ya and a B1 24-26 LAB .....Have fun

I needed a new transom and raised mine 2" from 6.5 to 4.5. Planing is different but not that much harder. Slip went way down and I picked up a good 8mph on top. The boat handles much better all around. I used 2" aluminum block to raise the front of the engines an equal amount. If you are doing the transom it would be silly not to raise the driveline in my opinion. You may need to do some hatch mods though. I also had minor issues with the rear gunwale and distributer. Great improvement to the boat for sure.

LMAO :drink:

6 blade on a bravo 1..lol are you kidding me..that drive will last about 5 minutes..I have a non stepped baja outlaw hull and we raised the x 3 inches, and I have way to much bow lift still with a bravo prop..and no extention box..

i have been using 6 blade herings on my imco sc drives which are the same internal parts as xr drtves for 4 years now and never had a problem .now i am going to 7 blade herings and raised my x a total of 7 1/2 inches

my baja 24ol was 5 1/2'' with the 2'' shortie handled better, than stock height was faster too. now the saber was the same think better at 5 1/2''. but I bought it unrigged with power or drive. I started out at 17 1/2'' = 3'' with the konrad ace xfactor drive and 8'' box. well it porpoised out of control, had to run 280 tabs down trimed in with a 5 blade. but it got on plane easy. today in 40degree temps we are trying 380 tabs, max 5 blade, px5, 1'' spacer = 4'', then a longer lower = 4 3/4'' driveshaft height. I am starting to think its balance, cause it gets on plane. these boats will propoise a little with no tab. so if I can get there ,then bring it up to 60,70,80, or wide open to see the slip #s. brett will lab the best prop. I hope I don't need a p5, transom lifting prop. can't find one to borrow. and its getten cold. already had to put the pink stuff in once:eek:. any ideas

A triple 47 Fountain and a single 271 are two very different boats, what works on the 47 might not work on the 271 at all. I would not compare the two.

x dim on a formula
 

I do a lot of x dim chandes and Formulas i would notch the bottom in about 10 inches.Raise the x so prop shaft is 4.5 inches below the vee and ru n a 4 blade Bravo 1.Remenber hatch clearance ,exhaust holes ,and the motor will have to be moved back as you go up ! Just talking from past projects we have done.

When you notch the bottom, how wide do you notch it? When you say 10", I assume you mean forward 10". How wide & how high is the notch? Anyone else with experience in notching transoms?