Driving an outdrive...

[ka0tyk]

So I took the boat out this weekend twice and it was flat enough to "enjoy" it. And by enjoy I mean put the stick forward more than just a few rpms. I cruise easily at 2500 rpms doing 30mph. I have a 23p mirage plus prop on a 1.62 alpha drive with a pretty mild 454, gas tanks were full. With the drive all the way down, the boat really buries the bow. I'm not sure if thats just the way the boat rides, etc. I dont have really ANY weight in the bow either. I havent even put floor over the stringers because I wasnt sure if I was going to make it open bow or not. When you trim the drive up, the boat attitude doesnt really change much. If I hit the throttle and the secondaries open up (vac carb, ugh) the boat comes to life but with the drive trimmed up I can hear and feel almost like "slipping." I trim the drive back down and again the bow is pretty low and i'm pullin mid 50's and not very comfortable with pushing it anymore...

any tips for where things should be and when?

 

[shintoooo]

Have you tried a different prop?

 

[wedge45]

Have you tried a different prop?

REALLY :yikes

Don't fall for the Different Prop routine on these boards.... they will eat you alive

 

[RiverDave]

Not sure what you mean by "slipping." When you have the drive down where was the water breaking? Ahead if the drivers seat? Behind? When you trimmed the boat, how much did you trim it (how long on the up switch?). And where was the water breaking?

Was the boat bow steering at all?

 

[obnoxious001]

So I took the boat out this weekend twice and it was flat enough to "enjoy" it. And by enjoy I mean put the stick forward more than just a few rpms. I cruise easily at 2500 rpms doing 30mph. I have a 24p rev 4 prop on a 1.62 alpha drive with a pretty mild 454, gas tanks were full. With the drive all the way down, the boat really buries the bow. I'm not sure if thats just the way the boat rides, etc. I dont have really ANY weight in the bow either. I havent even put floor over the stringers because I wasnt sure if I was going to make it open bow or not. When you trim the drive up, the boat attitude doesnt really change much. If I hit the throttle and the secondaries open up (vac carb, ugh) the boat comes to life but with the drive trimmed up I can hear and feel almost like "slipping." I trim the drive back down and again the bow is pretty low and i'm pullin mid 50's and not very comfortable with pushing it anymore...

any tips for where things should be and when?

Any of the outdrives that I have either driven or been in, either race boats or pleasure boats, you would take off with the drive all the way down to put the boat on plane, and then trim up a bit at time until you feel the boat free up and riding properly.

Do you have a trim gauge?

Did you look behind the boat when you say you felt it "slipping",, maybe the drive was up far enough that the prop was throwing a tail?

 

[dave29]

You need to find the neutral drive position. With the boat on the trailer and the drive down, run a straight edge under the bottom of the boat and compare the angle to the drive to the straight edge. Move the drive up until the drive is at the same parallel angle at the bottom. Check your trim indicators. Where the indicators are, trim wise, is the neutral drive position. This is the approximate trim setting for turning. When you take off, put the drive all the way down. Once on plane trim up to the neutral position. Next, continue to trim up until you feel the bow lift and again check your settings and the rooster tail of the boat. Check your tach and speedo above the neutral position as you are trimming and when the rpm's increase but the speed stays the same is about the top of the trim range and where you should be at full throttle in my humble opinion.
I know that on some of my boats a number as high as 8 was the neutral position.
Goon luck.

 

[boatnam2]

I have always done it the same way, when taking off always trim it all the way down and start trimming up while your picking up speed, your ass will tell you when its right at any moderate speed....Running wide open trim it until rpms drop off bump in back down a pinch and your golden. I dont think i have ever looked at a trim gauge in a boat going 60 mph or less.

 

[BigSteve]

You need to find the neutral drive position. With the boat on the trailer and the drive down, run a straight edge under the bottom of the boat and compare the angle to the drive to the straight edge. Move the drive up until the drive is at the same parallel angle at the bottom. Check your trim indicators. Where the indicators are, trim wise, is the neutral drive position. This is the approximate trim setting for turning. When you take off, put the drive all the way down. Once on plane trim up to the neutral position. Next, continue to trim up until you feel the bow lift and again check your settings and the rooster tail of the boat. Check your tach and speedo above the neutral position as you are trimming and when the rpm's increase but the speed stays the same is about the top of the trim range and where you should be at full throttle in my humble opinion.
I know that on some of my boats a number as high as 8 was the neutral position.
Goon luck.

You are spot on,
We do the same thing to measure prop height and locate the neutral trim setting

I prefer the Stainless Marine cable operated system over a trim indicator switch
for accuracy

The OP didn't say what prop he was running.

 

[ka0tyk]

You are spot on,
We do the same thing to measure prop height and locate the neutral trim setting

I prefer the Stainless Marine cable operated system over a trim indicator switch
for accuracy

The OP didn't say what prop he was running.

yes i did. mirage plus 23p.

 

[ka0tyk]

You need to find the neutral drive position. With the boat on the trailer and the drive down, run a straight edge under the bottom of the boat and compare the angle to the drive to the straight edge. Move the drive up until the drive is at the same parallel angle at the bottom. Check your trim indicators. Where the indicators are, trim wise, is the neutral drive position. This is the approximate trim setting for turning. When you take off, put the drive all the way down. Once on plane trim up to the neutral position. Next, continue to trim up until you feel the bow lift and again check your settings and the rooster tail of the boat. Check your tach and speedo above the neutral position as you are trimming and when the rpm's increase but the speed stays the same is about the top of the trim range and where you should be at full throttle in my humble opinion.
I know that on some of my boats a number as high as 8 was the neutral position.
Goon luck.

ill give this all a try. makes sense. i have a gaffrig trim gauge. similar to this one but white

so once i find a "neutral" is there a way to clock the trim indicator on the drive so that i can align it with a mark on the gauge?

 

[boatnam2]

What boat and motor?

 

[ka0tyk]

What boat and motor?

21' bahner. 454. alpha one gen 2 with a 1.62 gear

(old pic with alum prop)

i was cruising 30 at 2500rpms. drive fully down.

 

[gqchris]

so once i find a "neutral" is there a way to clock the trim indicator on the drive so that i can align it with a mark on the gauge?

Sure is, I circled the round Merc puck thing on the side of the drive. You just loosen the set screw and turn while you have someone watch the gauge on Dash. I realign my once a season or so Hope that helps.

Chris

 

[Havasu Hangin']

I'd also make sure there's no hook in the bottom.

 

[BajaMike]

I have always done it the same way, when taking off always trim it all the way down and start trimming up while your picking up speed, your ass will tell you when its right at any moderate speed....Running wide open trim it until rpms drop off bump in back down a pinch and your golden. I dont think i have ever looked at a trim gauge in a boat going 60 mph or less.

I agree with the above......but also you don't say what your wide open throttle RPMs are. If you can't get easily to around 4800-5000 RPMs when properly trimmed you are over propped. Your performance will suffer and it's really hard on your engine and especially on that Alpha drive.

Good luck!

 

[boatnam2]

I think i would get a nice 4 blade and have the 3 eared deal as the spare.

 

[BajaMike]

21' bahner. 454. alpha one gen 2 with a 1.62 gear

(old pic with alum prop)

Did it act any better with the alum prop??

 

[CampbellCarl]

Any idea where the cav plate on the drive aligns to the hull bottom? Just in the pix shown, seems like the X dimension is VERY low.

 

[Classic Daycruiser]

I have a gauge, and Alpha Drive on my Eliminator. I took it in for service to have the trim sensors replaced, which required the drive to be partially removed to gain access. Merc authorized dealer performed the work.

The boat did the same thing your describing, after the sensor replacement. The shop could not figure it out. Told me it was a boat hull issue. Took it to Eliminator a few months later, and had them look at it, since it was their hull. Eliminator fixed it. Said the guy who installed sensors was an idiot. They did not go into much detail. Eliminator has some incredibly sharp talent running around that place. Worth the extra $4 and hour.

 

[ka0tyk]

Did it act any better with the alum prop??

i suppose i could swap it out and see what it does. i have no clue what prop it is i cant find any markings on it.

 

[ka0tyk]

Any idea where the cav plate on the drive aligns to the hull bottom? Just in the pix shown, seems like the X dimension is VERY low.

not sure ill have to see. i cant put the drive all the way down on the trailer right now. with a LOW X dimension (the boat came this way from the time it was built) would that cause the bow to be pushed down and little lift when trimming up?

i dont have a WOT rpm right now. I wasnt really comfortable going much past 4k or so with the bow that low.

How do you know a prop will raise the bow versus lift the transom? I've heard some props do better than others in regards to lifting or carrying. I dunno if I would step into a 4 blade, like a bravo one without stressing the drive.

 

[boatnam2]

I have pretty much the same set up, My drive is not even close to going all the way down on trailer....Try a few props, do a few holeshot first one all the way down, next one a quick bump up on trim, next one 2 bumps up on trim, you will no within minutes were you want to take off from. Trimmed down and buried at 4k sounds about right trimmed her up should be around 4800 and riding nice, sounds like it cavitating give it a quick bump down. Might want to practice with half way decent water until you get her trimmed high and letting her fly

 

[BigSteve]

yes i did. mirage plus 23p.

Yes, you did say what prop you were running.

I have had more than one prop hub slip on me
something to check

You have a nice 21' rig.

A set of Bennett hydraulic trim tabs would complement it
Very nice for slower speed running in the ocean
or pulling kids on a tube/board at the lake.
Allows you to get a taller prop on plane.

I would give BBlades a call they offer many different styles of props
They may have a couple ideas on what prop would work best on your combo

 

[ka0tyk]

Yes, you did say what prop you were running.

I have had more than one prop hub slip on me
something to check

You have a nice 21' rig.

A set of Bennett hydraulic trim tabs would complement it
Very nice for slower speed running in the ocean
or pulling kids on a tube/board at the lake.
Allows you to get a taller prop on plane.

I would give BBlades a call they offer many different styles of props
They may have a couple ideas on what prop would work best on your combo

thanks. i have these laying around. just wanted to make sure i needed them before i drilled the holes... and where on the transom to actually mount them. horizontal or parallel to the bottom... etc.

 

[BigSteve]

not sure ill have to see. i cant put the drive all the way down on the trailer right now. with a LOW X dimension (the boat came this way from the time it was built) would that cause the bow to be pushed down and little lift when trimming up?

i dont have a WOT rpm right now. I wasnt really comfortable going much past 4k or so with the bow that low.

How do you know a prop will raise the bow versus lift the transom? I've heard some props do better than others in regards to lifting or carrying. I dunno if I would step into a 4 blade, like a bravo one without stressing the drive.

Our team is always prop testing ! Just because one boat had excellent results doesn't mean it will work on another. So take your time and test with a hand held GPS. Make a RPM and speed table. max rpm
Note the hole shot and overall feel of the prop.
We tested over the weekend with 4, 32 pitch props that run within a couple mph of each other on our boat
On a friends boat 3 didn't work at all, the last was 11 mph faster with a Yamaha TXP

You have a deep x -dim running a fully submerged prop. I think the bravo may have more blade dia and surface area than you need and it will effect top end.
But test with it. The more data you can give the prop shop the better.

A smaller dia 4-5 blade Hydromotive ? call Brent
A Yamaha prop ?

 

[Fun Times]

Mirage plus 23p.

Typically speakinng on performanc boats, a Mirage plus doesn't like to work so well on an alpha stern drive due to the diameter differences between the lower gear housing and the propeller. The propeller is bigger in diameter in turn usually interrupting the water flow between the two giving you less overall efficiency.,

The Mirage normally works better on the bravo drives while the smaller diameter Vengeance propeller from Mercruiser typically works really well on the alpha drives.

 

[boatnam2]

I have had a few mercruiser/alpha combo's and i thought the 5 blade worked very well also with that combo....What kind of ponies do you think your making 400?

 

[boatnam2]

Seen a few pretty decent high fives or revolution 4's for less the 200 bucks on e-bay....

 

[RiverDave]

I have a gauge, and Alpha Drive on my Eliminator. I took it in for service to have the trim sensors replaced, which required the drive to be partially removed to gain access. Merc authorized dealer performed the work.

The boat did the same thing your describing, after the sensor replacement. The shop could not figure it out. Told me it was a boat hull issue. Took it to Eliminator a few months later, and had them look at it, since it was their hull. Eliminator fixed it. Said the guy who installed sensors was an idiot. They did not go into much detail. Eliminator has some incredibly sharp talent running around that place. Worth the extra $4 and hour.

This is a possibility.. Kayotk do you have a dj gel switched for trim that will raise the drive all the way up? Or do you have a trim switch that goes to a point and then you have to hit a second button (trailer) to go higher?

If it is setup like the second it could be that the sensor is positioned incorrectly and stopping the up trim prematurely.

 

[ka0tyk]

This is a possibility.. Kayotk do you have a dj gel switched for trim that will raise the drive all the way up? Or do you have a trim switch that goes to a point and then you have to hit a second button (trailer) to go higher?

If it is setup like the second it could be that the sensor is positioned incorrectly and stopping the up trim prematurely.

I have my trim pump wired without the limiter as I didnt want yet another hole and switch in my dash when I could just hold the button down longer. My rexmar trim switch on my throttle doesnt have a trailer button.

I'm gonna try finding a place where I can back the trailer off off like a curb or something so I can drop the drive down, etc and 0 out my trim gauge.

 

[CampbellCarl]

I can't help but thinking that the addition of the BBC over the SBC has moved the boat's center of gravity enough to cause issues. Any guesses or known weight difference? 200? 300? right on the ass end of the boat would move the CG back how far?

Couple that with a low X dimension and I'm thinking that boat is plowing big time no matter the trim settings. I do have a high 5 21P that you can try.

Bilgie likes to use the phrase in fun but I really do think that this can be solved with props.

 

[530RL]

I'm with Carl's guess on the weight and x dimension, but who knows.

If you can't get it worked out with a prop, there are Alpha SS drives around which reduce the x dimension by 2.5 inches. It has a shorter upper.

 

[ka0tyk]

I'm with Carl's guess on the weight and x dimension, but who knows.

If you can't get it worked out with a prop, there are Alpha SS drives around which reduce the x dimension by 2.5 inches. It has a shorter upper.

The ss drives are hard to find and I hear parts are even harder. If I had to go that route I would just do a bravo with a shorty. At least then I wouldn't have to worry about breaking anything.

 

[530RL]

The ss drives are hard to find and I hear parts are even harder. If I had to go that route I would just do a bravo with a shorty. At least then I wouldn't have to worry about breaking anything.

All fair points. I was just trying to keep the weight down. You put a Bravo on that and your center of gravity goes even farther back.

Besides, you are an excellent wrench. Another challenge would be good.

 

[CampbellCarl]

All fair points. I was just trying to keep the weight down. You put a Bravo on that and your center of gravity goes even farther back.

Besides, you are an excellent wrench. Another challenge would be good.

It's further.....at least with regard to the 'orientating' (RD's word not mine) of the drive.....

 

[mjc]

I had a Caliber 1(which was the same bottom I believe) and my best prop was a Hill 4 blade that was smaller diameter, 14.5 inches I believe. The smaller diameter might be easier on the outdrive. It had a lot of bow lift because my 12 year old son could tell just by riding in it when I put my 23 mirage prop on, it rode that much worse. I think 14.5 is the size for the big outboards.

 

[ka0tyk]

All fair points. I was just trying to keep the weight down. You put a Bravo on that and your center of gravity goes even farther back.

Besides, you are an excellent wrench. Another challenge would be good.

Would doing a belly tank 2-3 feet further up than the existing gunnel tanks help move the weight forward? I kinda want to do that next...

 

[BigSteve]

Would doing a belly tank 2-3 feet further up than the existing gunnel tanks help move the weight forward? I kinda want to do that next...

Trim tabs will really help a ass heavy boat holeshot and lower planing speed

Moving weight forward hurts bow lift and kills speed

 

[AzGeo]

Transom angle also effects the 'drive trim angles' and the 'leverage the hull sees'. A 454 with an ALPHA at 1.62 gears is not a normal combo. 454 ALPHAS usually had 1.32 gears, to relieve torque stresses on the cases. If your transom is less than 15 degrees to the keel, the drive leg does not want to 'trim down enough' to give a nice controlled hole shot. On older hulls like Howard 21/Spectra, and most older jet boats that had 12/9/90 degree transoms, I would install a '5 degree wedge' when sealing up the transom piece to the hull. This requires the motor to be mounted 'a little bit higher, but the overall performance gains outweigh the money and effort to install. When I did custom rigging for Howard Brown, (at my shop) I used the 5 degree wedge and NEVER needed trim plates of any kind for any reason. If you have enough 'down trim', I would set the throttle at 4000 RPMs (as an example), make sure you have plenty of running room. As the boat rolls over and lifts the tail, start to 'trim up'. I trim up in 'clicks' and this way lets me FEEL what the boat wants and not guess at what is parallel or up from the keel. You need an accurate tach and speedo to do this kind of test. Go to 4K (steady state throttle opening) give the trim 'one click up' and observe the hull performance. Do this 'one click at a time' until you FEEL the sweet spot, where the revs are stable, the hull rides smooth, and the boat feels loose on the water. You may need to 'overtrim' to go beyond the best point but then all it takes is 'bumping back down' one click at a time until the hull speeds up and the RPMs become stable. Good luck ....

 

[530RL]

It's further.....at least with regard to the 'orientating' (RD's word not mine) of the drive.....

Wes is weeping right about now

[video=youtube;xSnraJOeOyM]http://www.youtube.com/watch?v=xSnraJOeOyM[/video]

 

[RiverDave]

I guess I am missing something here.. He is complaining of a plowing condition.. Why would you want more down trim with a wedge? Or pushing the CG forward with a gas tank?

 

[Nord]

Any idea where the cav plate on the drive aligns to the hull bottom? Just in the pix shown, seems like the X dimension is VERY low.

This is exactly what I saw. Of he is trimming up and the prop is blowin out it could be because the z is low right ? The weight of the front of the boat is too much for the prop when it's that low.

 

[Carlson-jet]

I would suspend the upgrades and spend the money on fuel and time with the fam. I have yet to to see a family picture captioned with "we got an extra 2 m.p.h. but had to cut the fun time short due to testing out the new 48 blade unobtainium prop".

Besides, the boat will perform far better with an all alum. 427" c.i.d. small block.
It's all in the bore spacing and lack of valve diameter. :thumbsup

 

[ka0tyk]

hrmm. same boat. alpha one SS with a 454. looks like probably the same prop. 23p SS.

http://quadcities.craigslist.org/boa/4437592267.html

so then having a low drive causes it to push the bow down?

 

[BigSteve]

hrmm. same boat. alpha one SS with a 454. looks like probably the same prop. 23p SS.

http://quadcities.craigslist.org/boa/4437592267.html

so then having a low drive causes it to push the bow down?

No!

Set up is everything in a boat.

This is what I think of your current set up
Nice family boat and a heavy bow to lift

Its has a heavy engine( sbc vs bbc) and the weak link is the Alpha drive
You want to be real easy with the power on that drive

Az Geo, is right about the transom wedge, the correct drive tuck in, on take off is easier on the drive.
And it will plane sooner with less bow rise.

Plates or both a fix/ tool in the box ! We have had to use them several times to solve
High X-dem tunnel set ups on the 22 Daytonas o/b. twin o/b and i/o's 4 people 112 gal fuel

Tabs can also reduces the drive stress the Alpha is seeing coming up on plane

The bow plowing at speed can be incorrect trim setting (to low) a prop with out enough bow lift

A hook in your hull can really screw up performance.

Place a long straight edge bow to aft on the last 3 ft of the running surface go back and forth with a light behind the straight edge if your seeing light measure it with a feeler gauge. Tap the bottom with a dead blow hammer listen for soft spots.