Phantom 21 outboard height opinions

Diablo · 11-06-2010, 08:21 PM

Hi there i would like some opinions on the bullet height on a Phantom 21 with a high performance outboard.
The outboard is a 2010 300XS with a Sportmaster gearbox.
I want obviously a good top speed and still keep a good amount of drivability.
There must be people with experience with this set up before so let me know your ideas.
Cheers

larby · 12-06-2010, 06:09 PM

General opinion tends to be level with the bottom, fixed to the transom.

That said, I'd imagine that'd give some issues getting on the plane 4 up, so I'd drop it a hole or 2, not like you're gonna be short on top end! John R is a few inches below and he still seems to be running pretty well, Edd is an inch or so below and he's fine too.

James

John.Richardson · 12-06-2010, 09:16 PM

hey Dave!

Mines a 20 not a 21 and am Definitely no expert on boat set up but here's my 5p-

Mines pretty low- prob about 3 inches below - but it seems to keep the boat pretty level and i almost always feel like I have good drive (except when the props not in the water

!!!) never had cavitation anyway other than the back feeling like it's sliding sometimes on turns.

My top speed doesn't seem to vary much whether just me on board or even 4 up and trimming out doesn't seem to add much speed either- just affects stability. It almost feels like the boat gets to that speed and then there's drag from the leg. I dunno if that is rubbish - just what I feel driving it.

Ultimately I haven't played with engine height yet but it seems to be working ok for me at the mo where it is. I do get chining above 65 when it's flat or a little bit of chop- hoping tabs may help?

Other thing that might be worth thinking about is torque steer- I hadn't really noticed it but my mate drove me in the boat the other day and I realised the boat leans over quite a bit when you open the throttle harshly - presumably more horses would mean that it would be more pronounced?? Mines mounted in the centre.

I know it's all specific to my boat and how it's set up but all I know I'm afraid mate!

Really looking forward to seeing the boat out racing- she's gonna fly!!

Are you planning on fitting a lifter?

John.Richardson · 12-06-2010, 09:23 PM

hey Dave!

Mines a 20 not a 21 and am Definitely no expert on boat set up but here's my 5p-

Mines pretty low- prob about 3 inches below - but it seems to keep the boat pretty level and i almost always feel like I have good drive (except when the props not in the water

!!!) never had cavitation anyway other than the back feeling like it's sliding sometimes on turns.

My top speed doesn't seem to vary much whether just me on board or even 4 up and trimming out doesn't seem to add much speed either- just affects stability. It almost feels like the boat gets to that speed and then there's drag from the leg. I dunno if that is rubbish - just what I feel driving it.

Ultimately I haven't played with engine height yet but it seems to be working ok for me at the mo where it is. I do get chining above 65 when it's flat or a little bit of chop- hoping tabs may help?

Other thing that might be worth thinking about is torque steer- I hadn't really noticed it but my mate drove me in the boat the other day and I realised the boat leans over quite a bit when you open the throttle harshly - presumably more horses would mean that it would be more pronounced?? Mines mounted in the centre.

I know it's all specific to my boat and how it's set up but all I know I'm afraid mate!

Really looking forward to seeing the boat out racing- she's gonna fly!!

Are you planning on fitting a lifter?

Burty · 13-06-2010, 06:34 PM

thats a big engine for a P21 dude, you'll need a big set of tabs to stop the hull trying to roll over with the torque of spinning a big prop! The problem with all these new engines is they dont rev so you will need to be spinning 27" , 28" pitch props and the phantoms are quite a narrow hull, ( i should imagine the P20 with the Rude is the same problem) the older 2.5 260 / 280 race engines were great as they could rev to 8k which enabled you to spin smallish props and running 15" mid sections so you could get the weight low down to stop the pendulem effect of having a large weight rocking from side to side

John.Richardson · 13-06-2010, 08:58 PM

Cheers burty- v interesting!

I have a set of bennet st16s waiting to be fitted- dave I'll let you know how I get on with them and if they help.

Maybe being mounted lower is a good thing then? Seems to work on my boat anyway.

Out of interest- how would the tabs help burty? Would you use them actively to try and dial out the torque steer or would just the greater running surface help?

Cheers

john

sean1982 · 13-06-2010, 09:03 PM

i would be interested to see how yours goes with tabs too john, as im thinking of getting some for mine.

Big Dutch · 13-06-2010, 10:17 PM

Fast Jonny-I am a little surprised to see your motor is mounted centre of transom.
Shouldnt there be an offset to allow for the torque ?

Up to 2 1/2 inches off centre ?

Renegade · 13-06-2010, 10:28 PM

Centre mounting is the best practise. Your height's really depend on what your intend on doing with the boat

John.Richardson · 13-06-2010, 10:53 PM

I dunno- I just drive it!!!!

like I said I hadn't really noticed till my mate had a go at driving- only really had any stability issues with the boat above 65 -

Burty · 14-06-2010, 09:33 AM

send wacky racer a PM he ran a 300xs on a P21 for a season and had loads of setup issues, then sold the hull and put the 300xs on a cyclone im sure he'll be able to tell you heights and props etc

I had tabs on my 20 but hardly used them as i never suffered from chine walking even at 90mph!!! only ever put 1 down if running side on with waves / wind and just used it to level boat up

Diablo · 14-06-2010, 09:50 PM

Cheers for all the advice guys i think that all just reinforces my assumptions so far but trial and error i think will be one of the best ways.
Going for a 27" prop to start and get a benchmark and fettle it from there.
Dave.

Toffy · 21-06-2010, 11:25 PM

A setup is always a personal thing. There are a lot of different opinions. It is my belief you must search what setup works best for you in certain conditions. I compare it to setting up a F1 car : 2 different drivers with different setups can go equally fast.

Best thing you can do is to ask people with the same hull/engine combination. That's the best starting point for your setup. As I read the posts above -> Wacky racer is the man to talk to !!

I give you my 5 cents for my P21 with 200hp Yam.
- jackplate 5 1/2"
- center mount
- centerline gearbox bullet is ideal at 1" below V

However this high engine height creates a cooling problem which you MUST solve.
As my engine doesn't have a low water pick up, I'll run it at 2-3" below V to keep it safe.

You will be allright with the 300XS as them gearboxes have low water pickups, and is equipped with a water pressure gauge... I guess

The downside of the 300XS is the weight is to high up as they only come in large shafts. This will give you a bit of a handling problem.

So, if you can handle it, and if the cooling stays OK, than you can keep raising your engine. I was told by a racer the ideal engine height was 1" below V...

Good luck, you have a very promising combination !
Remember, Wacky racer and Burty are the people to talk to. They are far more experienced than I am.