21' Scarab Prop Selection
 

Hey guys, struggling to find a starting point to select a prop. 1985 Scarab 1 21' 3200lbs dry ~4000 loaded. BBC 560hp@5200 630tq@4100 bravo 1 drive, wide trim tabs

Picked up the boat last year with stock 454 330hp mag w/ alpha 1 - I never ran the boat so I don't have a baseline for comparison. Came with a 21" 4 blade. New to I/Os and am clueless which prop to start with - I know it is mostly trial and error but need a starting point. Reached out to bblades a couple weeks ago with no answer, I'm assuming they are pretty busy this time of year

I was thinking a bravo FS 26" but thinking maybe 28-30" would be more suitable for my weight/power? Not looking for every last MPH, an all around one would be great. Diameter? Pitch? Blade #? Any suggestions welcome, thanks!

I think the short tube on the FX will not give enough stern lift to get the entire boat up out of the water making it sluggish and excessive slip.

That is a fair assumption, I was wondering if the short tube would hurt overall performance - do you have a better prop in mind?

What outdrive ratio? Assuming 1.50:1?
If so, I think you might be surprised how much power a 26" Rev 4 will soak up. IMHO that would be a good starting point. Maybe a 25" Mirage Plus but you'd likely hit the rev limiter with that. The ***** of it all is...props are still hard to find, generally speaking. A few months ago it was a year wait for new props from Mercury.

Checkmate,

Try a Bravo28 to start with. You're 1600lbs lighter than I am, and that's what I'm pulling with what I'd guess is similar power (ProCharged 496HO). I'm gonna guess you're gonna be in a 30 or maybe even a 32 before you're properly loaded.

Thanks. Brad.
(937)545-8991

You are correct, 1.5 ratio drive - and so ive found out! props are getting few and far in between but thankfully I have another couple of months to search

Thanks Brad, I figured it would start to inch up into that range, I am going to keep my eye out for a bravo 28 and see if I can snag one up. It seems like the best all around prop without much compromise

Checkmate,

Not knowing anything about your hull, and just going buy weight, I’m betting you’ll bury the rev limiter with a B28.

Keep your eye out. A B28 just popped up and sold here on OSO. Post in the “Wanted” section you’re looking for one. You might be surprised.

One more thing…. I hope you upgraded the outdrive….

Thanks. Brad.
(937)545-8991

I hope you installed external hydraulic steering! It will be a must in a small hull with that power level. Will be very hard to control any chine walk and properly balance the hull on the keel without it.

Small light fast boat, i don’t see stock outdrive being an issue. These are quick/fast without lots of power.

Speaking of which, did some history digging and saw where 500hp puts these boats near/at 80. Found a 383 near 500hp and a 525efi as example.

I don’t know these with bigger motors, I just work on a bone stock Scarab 1 with 260hp alfalfa 1.47 drive. Swings a 21” cleaver no issue unless overloaded with peeps and coolers. Then will throw a 19” on it. Either way, boat needs tabs to plane better.

I’d start with a 28” bravo , you may not want to go faster anyway ? I dunno.


https://cimg5.ibsrv.net/gimg/www.off...da24aa37d.jpeg

SB,

I had a B26 on our PQ while the injectors were giving us fits. After getting them straightened out, we took the boat to the lake to test them out. I couldn't get much above 2/3, maybe 3/4 throttle without bumping the rev limiter. When I reacquired a B28, I can now bury the fun stick and the engine loads out right at 5K RPM.

I'd much rather not be able to use the top end of the throttle range because my knuckles can't get any whiter, rather than because I'm afraid of a rod through the side of the block. Just sayin'... :ernaehrung004:

I didn't catch that the OP had upgraded to a Bravo drive. I thought he was still running the Alpha. All good.

Thanks. Brad.
(937)545-8991

I saw that posting! Too bad I didn't catch it a bit sooner, that guy got a great deal! Stock bravo for now, I'll keep you looped in to what happens with it, will be light on the throttles - again thanks for your replies and insight

I have one added to the cart as we speak, I want to run it stock before I pull the trigger it. I heard this hull gets a bit loose after 65-70mph so I don't plan on pushing it past that often. Will 100% upgrade to external steering in the future, though. Great advice

I'd rather have a bit too little prop than too much when starting out, glad to hear the b28 is working in your situation. I'll start with one of those and go from there. May very well end up with a 30 or 32 depending on how it spins

Checkmate,

Yup. Creeping up on it is definitely a wise approach. There are those who might suggest you've got more HP than the hull can handle. I call BS on that. I grew up on a 21' Nordic daycruiser with a 482/6-71/V-drive that my dad affectionately call the "Homesick Angle". It would easily plane off at 2200RPM and could maintain plane at 1900. At 6200 RPM, we were tickling 85MPH and running about as dry as a boat has any right to. Your numbers are going to be different, but I think you're gonna be in that same realm. It's gonna be a hoot. You built all those HP. Now ya gotta load 'em up. I'm betting you're going to spin a B28 like it ain't even in the water. Curious to see how it goes and where you end up.

Thanks. Brad.
(937)545-8991

That nordic sounds like a screamer! 85 in a 21' seems pretty scary, better have some steady hands! Do you think a 5 blade would be fine in my situation? There is a decent deal on a 5 blade 28" near me, comparatively to new props, at least

Doubtful. Most likely your drive is deep in the water. Most small boats with Alfalfa’s where. This is assuming you didn’t raise drive height when you installed Bravo. Or did you ?

Correct, didn't change the height at all, x dimension should be the same. Lower unit has low water pickup, not dual side, but I heard it's the same aside from that change. I should stick to 4 blade?

5 blade is typically for high x dimension when a 4 blade is not grabbing enough water and slipping. Small performance boats don't usually need a lot of blade area. Many run 3 blades also.

Checkmate,

This....

On our Rinker 236 we had before the PQ280, we bought it with a 22P 4B of some unknown make that had been reworked to 21P. The boat rode really wet, and maxed out at about 51MPH. We switched to a 23P 3B of an unknown make (it was an even "try it, keep it if you like it" swap) and the boat came alive. It rode on it ass like it was supposed to and topped out at 60MPH even.

You might try a Mirage Plus 27 or 29P. I'm still betting you'll be over 30P before the engine is happy.

Thanks. Brad.
(937)545-8991

Spot on, props :lolhit: to you both for chiming in - a few market places have a testing period that I'll take advantage of. Starting with a 28 4 blade and potentially moving to a 30 or 32 as needed. Maybe in the future my curiosity will get the best of me and mess with a 5 blade to see what happens for ****s and giggles

Checkmate,

It's a solid hob, but it is a cheap test for a 3B prop.

Mercury Marine Mirage Plus 48-821720 a50 29p | eBay

Thanks. Brad.
(937)545-8991

Good find - I find a lightly used 4B B1 28" prop, I am talking with the seller and should hopefully be able to pick it up. You mentioned solid hub, from my understanding, is that not required when you are talking about higher horsepower applications? Ive read that 400hp is the line between rubber and solid hubs. Would love to know more, as the props im looking at are all solid

Checkmate,

Personally, I prefer the props with a sacrificial hub. It's pretty much just a failsafe to prevent breaking or bending the shaft. Yes, at some point, HP/torque is going to dictate a solid hub. I don't think there's anything wrong with either, aside from overpowering the sacrificial hub.

I posted this Mirage Plus because I think your boat is going to be happier with it than the Bravo. This is merely an opinion based on empirical experience with our Rinker. As I understand it, the Bravos are considered "lifting" props, and I'd bet your hull doesn't need any transom lift, and, in fact, will ride wet like our Rinker did.

Thanks. Brad.
(937)545-8991

Thanks for the info, I figured only solid hubs would be suitable for my power - if I can get away with rubber hubs that helps open the search a bit. I sent that seller a message to see if they would be willing to ship, as it is local pickup only for now. For only $350 its hard to pass that up, and worth trying at a minimum! In addition, Im still going to pick up a 4B as well to compare the two, as it never hurts. Will keep you updated!

Is it really a rubber hub, or the replaceable type?

I won't ever do rubber hubs again. Every one I bought used, spun. i then had it re-hubbed. Ended up spending more for the used POS old prop than buying new.

Xlint,

All of mine have been some sort of hard plastic that pressed into the prop and a brass (?) insert that splined on the shaft and keyed into the plastic sacrificial hub.

While I've never needed any of it, I keep a spare prop, sacrificial hub, brass insert, a couple castle washers and prop nuts on the boat.

Thanks. Brad.
(937)545-8991

The 3 blade seller never responded. Ended up buying a standard Bravo 1 28" - figured it's a safe enough point to get me on the water then I can start experimenting. I'll do more research on hubs, but leaning towards solid due to some of the stories I've heard with the non-solids

Don't sweat the replaceable hubs like the Flo Torq from merc. Those can use a plastic for lower HP or they have a "solid" aluminum one for the higher HP engines. Either one can be installed/replaced into the prop.

https://www.ebay.com/itm/31207122832...3ABFBM_Lmr6fJh

I specifically will not use the "old style" rubber hubs any longer. Those are what i was having problems with.

They look like this. https://www.ebay.com/itm/36413309060...Bk9SR7y6zenyYQ

Be very careful with the 4 blade we built a 22 Scarab with a 525 and bravo shorty on ITS and could not run a 4 blade it would pick the back of the boat up and bow steer badly. we ended up with 27 pitch 3 blade mirage

Checkmate,

This is still my thinking, only higher in pitch.

Thanks. Brad.
(937)545-8991

thanks for the heads up! So you think that hub you linked would be sufficient? If so I will go ahead and send in an order!

The first link is for the lower power hub. However, someone mentioned they run them as it's the weakest link in the drive system should you strike something with the prop.

This is the "solid" hub kit for 400+ HP

https://www.ebay.com/itm/23373104311...Bk9SR6SUhcPzYQ


I am not experienced to recommend anything to anyone. I'm just trying to help out where I can.

Can you tell more about your experience with that 22 Scarab? I have a 22 Scarab with a 548, XR drive, and started with a 30p Bravo prop. Like you experienced, it would bow steer very badly. A buddy had a 26p Bravo 4 blade but it was a lefty. I tried it just to see, and it calmed the boat down a lot and worked decent, but would make the boat list to the right. Next I tried a 27 Mirage plus, and the boat was awesome in every way, until you got to 73mph or so. Then the prop would blow out, every single time. This was the best prop I tried on it to this day. It carried the bow well, was super stable, etc. But I kept looking because of the blowout. The prop had a vibration to it, so I am thinking maybe it had a bent blade (can't visibly see anything wrong with it).

Since then I tried a Hydromotive 4 blade cleaver and it worked well for top end, but had a lot of slippage in lower and mid cruising speeds so I didn't like it. The 27 Mirage would do 70mph at 4,000rpm.

Later yet I got an Imco -2 shorty and a out of the box stock Bravo 28p four blade. You have to finesse a little to get it on plane, and it has a lot of slippage at speeds under 40mph or so. In the lower 70s it is gaining speed as you are trimming, then the boat will start to curve to the right and you have to trim it back down some so can't really go any faster. My boat does not seem to have gained anything from the shorty and it does seem to like the 3 blades better. I would like to try another 27 Mirage plus that is known to be good and see if I still experience blow out at high speed.