Engine height

[Jonnyboy]

Any comments on the height of the engines??

[Taz]

Looks a inch to high to me but im no expert ive always fought the bullet should be in line with the bottom of the boat

[Jonnyboy]

Theye have a set back of 6 inches whether that makes a difference?

[TheMutzNuts]

Cye says that for every 4" setback you go up 1"

[Matt]

Running 2 high has a number of side effects:
1) Loss of water pressure
2) Loss of bow lift
3) Difficulty getting on the plane.
4) Loss of drive in the rough

But the upside is el maximo speedo in the flat.

2 high, 2 low. Dunno till you've tried it. If it were me I'd start conservative and go a bit lower, then jack em up if needed.

[Jonnyboy]

That looks about right then.

Thanks

[Burty]

Jay Smith on scream and fly (the guy building my engine) says


Propshaft height from pad

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I have always used the formula for every 1" you go back you can go up 1/8" from split shaft..... In otherwords if you have a 8" plate you can ( in theory ) come up 8/8 ths or 1 " If have used this formula on many different configeration hulls and its been pretty close give or take 1/4"........You need to remember all hulls have thier own sweet spots and its got alot to do with the layup weights and the load its carrying...


Good luck !

Jay

[JamesM]

Originally posted by Taz
Looks a inch to high to me but im no expert ive always fought the bullet should be in line with the bottom of the boat

Don't forget its a twin, so its the bottom of the boat directly infront of each motor and not the bottom of the V. Bearing this in mind its actually very difficult to judge the engine heights from that side on 2D photo.

[Jonnyboy]

Originally posted by Johnny Boat Dude
Don't forget its a twin, so its the bottom of the boat directly infront of each motor and not the bottom of the V. Bearing this in mind its actually very difficult to judge the engine heights from that side on 2D photo.

I have placed a straight edge along the underside of the hull to the torpedo of the gearbox. Theye are 3/4" up & the engines are set back 6". I am not to bothered about top end more so the handling, (this should be a good rough weather boat) I have put strenghtheners from the transom through the splash well then bolted through the Knees.
All i know is that it ran a few years ago with CLE boxes but I do not know what it ran like, it was the P25 @ DB Marine


John

[John G]

Looks like an OK starting point - if not a good final position - only testing will tell for sure!

If yr going to bias the boat towards better rough water handling (vs out & out speed) then make sure you've got some room to manouvere the engines down some more. Then if yr initial testing gives unsatisfactory handling its easy to drop the engine down to the next hole on the saddle.

Hope this helps - let us know how it goes

BTW what's running from this pick up?

[Jonnyboy]

Gaffrig Speedo & Thanks for the Info

John

[Adam]

All looks pretty good Jon - don't think you will have any major problems, water pressure should be good. If handling is out at all you may look at going a little lower as you should have plenty of top end anyway.

Probably all going to go down to what props you run and getting those dialled in.

Adam

[Jonnyboy]

Cheers Adam

Prop's what a choice I am thinking about a 5 blade clever but am open to Suggjestions but it really depends on how many people are willing to lend me a pair of props until I get the right one!! but that will be next year

John

[roofer]

ive got a pair of 24 and 28 choppers your welcome to borrow

[Jonnyboy]

Thanks I will take you up on that when I get there.

John

[ToffenG]

Hi!

Glad to see someone else also rigging twins on a Phantom 25! I am also in a process of mounting twins on my 1985 Phantom 25. It will either be 2 x Merc 2.5 or 2 x Promax 300 SVS.

I have been reccommended to mount the engines 23 inches senterline to senterline. How far is your engines mounted from eachother?

Merc Hi Performance reccommend a engine mounting height of 7 inches - 8 inches using twins in excess of 90 mph. This translates to a propshaftheight of approx. 1 inch below - even with the bottom. So you should be on the spot there.

If I am to use 2 x PM 300, I have to mount the engines as close as possible to the transom due to the overall balance. Then the mounting height will be cruical. I have to find a balance between rough water handling and top speed. I presume 1 inch below will be the solution for a start.

What kind of speed do you expect from your rig? Any pictures?

Cheeers from Norway!

Toffen G

[Captain Chaos]

Toffen.

how far are you into this project?

[Burty]

by the sounds of it not very far if he hasn't even got the motors yet

[ToffenG]

Hi!

I had twin Merc 2,5 SS engines available this spring, but due to the taxman, I had to postspone it some months.

I have 2 x Merc 2.5 with 20 inch midsections available now, but then I have to sell my PM 300 SVS. Therefore I may buy a nice 2000 PM 300 (run in fresh water only) with 20 inch midsection and sportmaster lowers.

I have through some research learned that the engines should be mounted 23 inches senterline to senterline (alien cowlings). I will use Latham / Marine Machine hydraulic steering.

If I am to use 20 inch midsections, I am afraid I am to low with the propshaft. The transom is 22,5 inches tall at 23 inches senterline to senterline. With a 20 inch midsections, the engine mounting height will be only 2,5 inches. Therefore the engines have to be lifted approx. 4,5 inches.... A 15 inch midsection (SS / Mad Efi) could be the solution. But then we may be too high. What do you think.

I expect a speed of 90 mph +. Should this be possible.

Here is a picture of the ol'lady.

Cheeers and thanks, Toffen G

[Captain Chaos]

I'm quite obviousely underqualified to answer those questions.

just a thought............dont bother with aliens if it makes set-up a problem. Also, havent people rigged Phantom 25's with 20inch mids before and had good results?

CC