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View Full Version : Looking for more speed: Blown 23' Scarab SCS



OliverM5
02-25-2007, 07:35 PM
Bought the boat 2 years ago and did a complete cosmetic restoration. Boat came with a Vortech Blown 502 (@ 5 lbs boost), XR Drive and 30 pitch prop. I've gotten it up to about 84 mph with this combo (1/2 tank gas and 4 people), but the boat did get a bit squirrely (chine) at that speed. Is the hull pretty much maxed out at these speeds or should I start playing around to get it into the low 90's? What can I do to get it there and without the instability?
http://www.***boat.com/image_center/data/522/P9020256_2_.JPG

Phat Matt
02-25-2007, 07:37 PM
Tabs would probably help.

OliverM5
02-25-2007, 07:39 PM
Tabs would probably help.
Got the 1000's on it already...they actually kill top end speed as they drag in the water, so they are no good for top end speed stability.

paradigm shift
02-25-2007, 08:26 PM
Tabs will help just do not drop them lower than the bottom.
I am no expert but I would say you are pushing the limits of that hull. Not to say you can not go faster but you are faster than 99% of the others that run that hull I would expect. So finding someone with expierence with that hull and speed will be hard to find.
I believe you will need to try other props or work with gettting your existing prop labbed to help. Drive height also has a lot to do with speed and how a boat reacts to or handles with a given prop. Have a prop that works well and you change drive height you may find it no longer works good. Other than thattake a straight edge and check the last 3' of the bottom for straightness. Sharp edge at the transom and bottom will help some.
Getting the maximum speed from any boat is expensive and a time consuming with a lot of testing before you find that perfect combination or set up unless you go with a known package.
Good luck on your quest and use a lanyard kill switch and llife jacket for those high speed runs.

OliverM5
02-25-2007, 10:00 PM
Paradigm, great input....I'll probably spend thousands and end up with a few mph (if even that)....I may just enjoy the boat as is...

76ANTHONY
02-25-2007, 10:01 PM
oliver im a be honest with ya, that boat will never go any faster so you should just hand me the keys and the pinkslip and give up on boating forever:D
joking of course, that is one cleannnnn azz boat, awesome job you did on it..props to ya:D

OliverM5
02-25-2007, 10:06 PM
oliver im a be honest with ya, that boat will never go any faster so you should just hand me the keys and the pinkslip and give up on boating forever:D
joking of course, that is one cleannnnn azz boat, awesome job you did on it..props to ya:D
LOL...thanks man...:D

C-2
02-25-2007, 10:42 PM
Start by adding Hyd steering. You already know the boat is loose, if something let's go at 80mph - you're gonna have some people in the water. Blown motor/heavy hull, 80+ and Bravo = a bad accident, waiting to happen. Besides, the steering will dress your boat up nicely ;)
If you really wanna see loose, put a nosecone on. Might get you a couple, but IME, they really loosen the boat up.
There are a few guys over at OSO who run the 23' - you should check there.

OliverM5
02-25-2007, 10:44 PM
Start by adding Hyd steering. You already know the boat is loose, if something let's go at 80mph - you're gonna have some people in the water. Blown motor/heavy hull, 80+ and Bravo = a bad accident, waiting to happen. Besides, the steering will dress your boat up nicely ;)
If you really wanna see loose, put a nosecone on. Might get you a couple, but IME, they really loosen the boat up.
There are a few guys over at OSO who run the 23' - you should check there.
Hydraulic steering already on the boat...I'll check out OSO :)

C-2
02-25-2007, 10:59 PM
Sorry, didn't see any external rams on the boat, must be single ram on the other side?

OliverM5
02-25-2007, 11:10 PM
Sorry, didn't see any external rams on the boat, must be single ram on the other side?Yup :D
http://www.***boat.com/image_center/data/522/P1010040.JPG

C-2
02-25-2007, 11:25 PM
Smart man :)
What year is that boat, it looks bitchen.

YeLLowBoaT
02-25-2007, 11:30 PM
Do you have anything on the bottum of the hual that might be cuasing drag?
I remember reading a artical a few years back about a larger go fast picking up about 12 mph by shaving 3/8" off its water pick ups...I was in a boating mag. ( I want to say power boat mag) Now I don't think you will have that kind of increase, but every little bit helps.

OliverM5
02-26-2007, 10:25 AM
Smart man :)
What year is that boat, it looks bitchen.Thanks man, it's a '98 :D

RiverDave
02-26-2007, 10:37 AM
Man what a great looking boat! I didn't even know Scarab made anything like that, small boat wise.. I tend to follow the west coast customs a little more though then anythign else.
When the boat started to chine walk, were you trimming up to let the boat fly? Did you have the tabs dropped at all?
I know on a few hulls that tend to chine out here, they'll actually mount the tabs differently. The put them more flat, so that you can lower them but just the outer tips are going to touch the water. If the boat rocks to the left, the left tab will dig in a little more and correct the chine walk, and to the right vice versa. With just the tips doing the work it tends to scrub off alot less Speed as well. With them mounted in there current configuration if you lower them your actually trimming the boat down closer up to the bow and that can potentially make chine walking worse, and eventually a potential bowsteering problem at speed.
I'm no expert, so take what I have to say with a grain of salt. I will say by mounting those tabs the other way you'll lose alot of the "bury the nose" in rough water capabillities that you have right now. Beautiful boat again, and good luck with your problems.
RD

Big Kahunaa
02-26-2007, 10:37 AM
that is a very nice ride i like the way you did it

playdeep
02-26-2007, 10:45 AM
Nice boat..
I think I would invest in dual ram hydraulic,instead of the single ram that you have.
Not sure if you have a straight V,or pad bottom.Might try different props,Some people have had good luck with the Hydomotive 4 blades.Talk to prop shops see what they recomend.
If you go dual ram,you can actually counter steer once the boat starts to chine,that basically entails moving the wheel back and forth an inch or so to counteract the side to side motion.
I have a blown 25ft. V,that runs about 95-98...depending on how brave I happen to be feeling.

OliverM5
02-26-2007, 10:54 AM
Man what a great looking boat!
When the boat started to chine walk, were you trimming up to let the boat fly? Did you have the tabs dropped at all?
RD
Thanks for the props...I've played with the tabs and they will cut off speed as soon as they touch the water...here are a few more pics:
http://www.***boat.com/image_center/data/500/P1010028.JPG
http://www.***boat.com/image_center/data/500/P1010039.JPG

AZJD
02-26-2007, 11:09 AM
Damn, super clean little boat. You have some sizable tabs on that thing. Be careful with those. They will cavitate theat boat in a second if down too much while turning.

Beer-30
02-26-2007, 11:38 AM
Heavy (well built, as Scarabs are) and non-stepped hull, I would say you are topped out. I wouldn't push a 23-footer into the 90s. If you want to approach (and pass) triple digits, you would want to invest in a DCB 28' Extreme (stepped V), a Howard 25 or 28 Bullet (stepped V), or pretty much any cat. Sponsons will keep you stable at those speeds (cats).

Fast Freddy
02-26-2007, 02:28 PM
put the tabs down until they stop the chine walking and then add another 100 hp to your motor. the increase in HP will counteract the loss of speed as a result of you tabs creating drag. this is my plan anyway with my nordic. i want 90 mph on gps out of my nordic and in order for me to get that kind of speed i am gonna need more power because i am already propped right with respect to my rpm range, etc. as it stands right now i have dual ram steering but i don't have tabs. my boat is chine walking at top speed so i won't throw any more power at it until i get tabs. safety comes first here. i know that the tabs are gonna scrub speed so more power is the solution imo. a hook generally creates porpoising and not chine walking. i run a lab finished prop which gives another 2-3 mph. changing the lower housing on your bravo drive to the more hydrodynamic race version will give you another 1-2 mph as well ( i have not done this yet becasue it is BIG bux). beyond that i would look to your x-dimension if you want more speed.

Beer-30
02-26-2007, 02:38 PM
If you change to aluminum heads, you would probably gain what you are looking for. I would think your Mag bottom end would be good for 6 to maybe (:idea: ) 7 pounds of boost.
AL heads would add more HP, even without other changes (although you might as well change the cam and add roller rockers) but it will also shave off 80 or so pounds.
You may also want to add a nice tubular header exhaust for another 30-40 hp - if boat is not already equipped. That will also shed weight. Shedding weight is like adding HP.

Havasu Hangin'
02-26-2007, 02:47 PM
Chine walk is caused by the stern lifting. Somtimes it's the hull's design- too much lift because it's past it's designed top speed (lifting strakes, pad, etc.), but sometimes a bow-lifting prop will help.
I actually have fixed chine-walking with a prop change before, but each boat is different (weight balance, x-dimension, etc.).

Fast Freddy
02-26-2007, 02:50 PM
If you change to aluminum heads, you would probably gain what you are looking for. I would think your Mag bottom end would be good for 6 to maybe (:idea: ) 7 pounds of boost.
AL heads would add more HP, even without other changes (although you might as well change the cam and add roller rockers) but it will also shave off 80 or so pounds.
You may also want to add a nice tubular header exhaust for another 30-40 hp - if boat is not already equipped. That will also shed weight. Shedding weight is like adding HP.
shedding weight also changes the center of gravity in yout boat. which in my case i will be putting on aluminum heads to offset the increase in weight that my trim tabs will add. the supercharger, intercooler, etc that i added to my boat really made the back of the boat heavy. i suspect that your 23' scarab is in need of a diet in the rear of the boat. do you have aluminum heads and lightweight headers?

Biglue
02-26-2007, 02:58 PM
With Freddy on the case, you should be smoking Cigs, MTI's, Nortechs etc in no time. :D

playdeep
02-26-2007, 03:11 PM
With Freddy on the case, you should be smoking Cigs, MTI's, Nortechs etc in no time. :D
...That's funny:D
Actually if you ran 84 w/4 people and 1/2 tank of fuel...try a speed run with 1 person,1/4 tank,no cooler etc,might put you in the 86-88 range.
How many rpm's are you turning with the 30p prop...?

Havasu Hangin'
02-26-2007, 03:14 PM
Actually if you ran 84 w/4 people and 1/2 tank of fuel...try a speed run with 1 person,1/4 tank,no cooler etc,might put you in the 86-88 range.
...and cold air and cold water (for the intercooler) with a slight chop (so I've heard...lol)
:D

Fast Freddy
02-26-2007, 03:30 PM
i bet if i were to get rid of the gold chain around my neck that i would pick up at least 3 mph.......

spectras only
02-26-2007, 03:40 PM
[b]Chine walk is caused by the stern lifting. Somtimes it's the hull's design- too much lift because it's past it's designed top speed (lifting strakes, pad, etc.), but sometimes a bow-lifting prop will help.
Ditto
The 23 scarabs ride high out of the water with bigger HP than the recommended factory rating;) . If you took a video of your boat , you'll see the chines are out of the water , running on the keel , hence the lowered tabs helping controlling your situation. Try a prop with more rake to lift the bow , let the stern dig deeper , supporting the hull on its chine. Imco shortie [ giving higher X dim ]would help lowering the stern in the water also, lot of $$$$$$. I had to turn my props in to lower my stern , because of the same scenario with my boat as yours . Watch this video , how my boat airing out with 4 people and full fuel . With the props turning out before ,it did lift the stern so much the boat chine walked like crazy , starting at 70 [ boat is well over 6000 lbs loaded ].
http://www3.telus.net/spectrasonly/ah.wmv

spectras only
02-26-2007, 03:51 PM
This is how the attitude of the 21' Scarab 1 with a 350 260 HP package supposed to run , with chines supporting the hull side to side .
http://www3.telus.net/spectrasonly/1985%20scarab%201.jpg
An adjustable rear wing could help keeping the stern down without speed rubbing trim tabs , hehe .
http://www3.telus.net/spectrasonly/scarab%2021%20XL.jpg

Run_em_Hard
02-26-2007, 08:06 PM
I know that the Tabs have already been brought up but I will bring it up again. I do believe that one of the Powerboat TV shows talk about the proper tabs, Reggie Fountain is host on that. They do need to be parallel with the water not perpendicular with the hull to reduce chim walk. I dont remember what 30p you said that you are running but a shorty might help some. If you are currently running a 3 blade that there is a good chance that one could help. I would call IMCO with the info on how deep your prop shaft sit realative with the bottom of the hull. Out of all honesty on my end I would have to say that any faster in that hull and you might be asking for trouble...

OliverM5
02-26-2007, 08:49 PM
I think my best bet would be playing with the prop (different type, labbing, etc). Also, my motor is a built 502, so I could up the boost if I wanted to - I assume I'd change the pulley, right?
How much increase in HP can I expect going from 5 lbs to 6 or 7 lbs boost? Will this reduce reliability and motor life significantly?
Right now I'm using a 4 blade bravo one 30P, what other props could help my case? Somebody mentioned "turn in" vs. "turn out" - what is that?

Beer-30
02-26-2007, 09:08 PM
I think my best bet would be playing with the prop (different type, labbing, etc). Also, my motor is a built 502, so I could up the boost if I wanted to - I assume I'd change the pulley, right?
How much increase in HP can I expect going from 5 lbs to 6 or 7 lbs boost? Will this reduce reliability and motor life significantly?
Yes, pulley changes boost. But, are you carbed or EFI? Fuel will have to go up with boost. Jets for the carb or fuel pressure for the EFI.

OliverM5
02-26-2007, 09:34 PM
Yes, pulley changes boost. But, are you carbed or EFI? Fuel will have to go up with boost. Jets for the carb or fuel pressure for the EFI.
EFI, JE pistons, hardened crank, ported heads....

spectras only
02-26-2007, 09:38 PM
Oliver , I dug up some articles on your boat. As you can see , the boat was outfitted with a 502 with 415 HP origionally .there's no mention of ill handling with that power , and with a light hull and more boost for power , you must be way out of the water riding on the pad , becoming unstable .14 1/2 X 25 Mirage Plus prop was used .
http://www3.telus.net/spectrasonly/scarab%20scs.jpg
Ps;Larry Smith design , Plexus bonding fiberglass stringer system , no wood used in the boat , not even in the transom . "It's a keeper".

OliverM5
02-26-2007, 09:42 PM
Oliver , I dug up some articles on your boat. As you can see , the boat was outfitted with a 502 with 415 HP origionally .there's no mention of ill handling with that power , and with a light hull and more boost for power , you must be way out of the water riding on the pad , becoming unstable .
Nice find! So the question is, how do I fix that issue, with a different prop or ?

spectras only
02-26-2007, 10:03 PM
Like I said before , you're running on the inner strakes [Wellcraft calls them speedrails] up to around 70 and after that is too much boat out of the water running, on the delta pad only. I'm no Scarab expert , but your boat has a similar pad design as mine and behaves similarly. My boat is practically a 24 footer with more power [ rare with twin package] than most 257 Mirages and needs more attention with drive/trim input than the singles. Prop testing can bring interesting results ,and that's what I would do first .You can see in the mag shot that the outer chine is practically out of the water with only 415 HP on tap .
I'm only going about 50 here with tabs level with the keel , props turning out , and the boat is airing out already .
http://www3.telus.net/spectrasonly/June%202505-166%20copy.jpg
http://www3.telus.net/spectrasonly/mirage%20in%20deep%20cove.jpg

spectras only
02-26-2007, 10:21 PM
Just reread your posts .You mentioned of a single external steering ram .
I'd suggest to upgrade to dual rams .

C-2
02-26-2007, 10:37 PM
Those are good numbers, you put some more ponies in it and you are in drive breaking territory?
Is a 23' 3700 lbs. considered light? My 21' is 2700 lbs.
Before you add any more power or crank up the boost, call up Inman at Imco - he'll tell you if you are encroaching upon drive breaking territory.
Besides, at 85, you are going to outrun most every 21-25 boat, and be outran by anything over that anyways since most have twins.

playdeep
02-27-2007, 10:34 AM
Nice find! So the question is, how do I fix that issue, with a different prop or ?
If you'd like to try a different prop...I have a labbed 32p bravo,that's been tweaked a bit.
I'll be in Havasu March 8-11...you are welcome to try it out.

DeepVee
02-27-2007, 12:36 PM
I'd try a Mirage+ or Hydromotive Q-IV prop. The B-1 has a lot of stern lift. A Mirage+ will be the fastest prop, Hydro will handle better but be slower then the M+. The B-1's have some funny characteristics on smaller V-bottom boats. You also may be able to drive through the chine walk and it'll calm down on the other side, takes some practice though. I wouldn't use the tabs to defeat chine walking. You gotta drive through it, knock the lean down with the steering wheel, steering into the lean, but it'll come back if you stay in the chine walk speed.

Beer-30
02-27-2007, 01:20 PM
reverse the drive and get an opposite prop?