Engine height
09-26-2006 | 01:01 PM
#1
Thread Starter
Registered
Joined: Oct 2000
Posts: 703
Likes: 61
From: Norway
Engine height
Hi!
I trust you are well.
I would be very happy if you could give me some advise on propheight. I have a Phantom 25 with twin Merc 2.5 EFI SS engines. The boat weight is 2.900 pounds with driver and 10 gallon fuel.
I have mounted the engines directly on to the transom. The engines have 2 inches built in setback in the SS midsections. Current propheight is 1,2 inches below the bottom. I use CLE lower units. 1.87 ratios.
I have only managed to test two different props; stock Bravo 28 x 14,5 and stock Mirage Plus 27 x 14,5. Top speed with the Bravos was 84 mph at 6.300 rpms and with the Mirage Plus top speed is 86/87 mph at 6.800 rpms. Over these speeds the boat requires more bowlift, and the props loose bite and rpms climbs.
I am spinning the props inward.
Bravo is a bowlifting prop, but the 4 blade create transomlift too. The Mirage Plus is a low rake prop with large blade area. I think these are the reasons why the do not fit.
Should I add 2 inch setback spacers? This will lower the propshaft 0,5 inch and give a little more lift. Balance is now perfect for high seas. Or is the correct prop the key answer?
Its very difficult to get hold of props to test here in Norway. I will try to get hold of two Chopper 28 props. Maybe a pair of ET's too. Or Raker props (which have to be machined to fit) ... What do you think?
Cheeeeers, Toffen G
I trust you are well.
I would be very happy if you could give me some advise on propheight. I have a Phantom 25 with twin Merc 2.5 EFI SS engines. The boat weight is 2.900 pounds with driver and 10 gallon fuel.
I have mounted the engines directly on to the transom. The engines have 2 inches built in setback in the SS midsections. Current propheight is 1,2 inches below the bottom. I use CLE lower units. 1.87 ratios.
I have only managed to test two different props; stock Bravo 28 x 14,5 and stock Mirage Plus 27 x 14,5. Top speed with the Bravos was 84 mph at 6.300 rpms and with the Mirage Plus top speed is 86/87 mph at 6.800 rpms. Over these speeds the boat requires more bowlift, and the props loose bite and rpms climbs.
I am spinning the props inward.
Bravo is a bowlifting prop, but the 4 blade create transomlift too. The Mirage Plus is a low rake prop with large blade area. I think these are the reasons why the do not fit.
Should I add 2 inch setback spacers? This will lower the propshaft 0,5 inch and give a little more lift. Balance is now perfect for high seas. Or is the correct prop the key answer?
Its very difficult to get hold of props to test here in Norway. I will try to get hold of two Chopper 28 props. Maybe a pair of ET's too. Or Raker props (which have to be machined to fit) ... What do you think?
Cheeeeers, Toffen G
Last edited by Toffen; 09-26-2006 at 01:03 PM.
09-26-2006 | 05:03 PM
#2
Registered
Joined: Aug 2002
Posts: 5,646
Likes: 9
From: Apache Jct. AZ
Re: Engine height
Toffen,
Unfortunately, I'm certainly not the guy that can give you any suggestions, but I always like seeing you guys from the "other side of the pond" showing up at our little watering hole here.
Good luck in your search, I'm sure a few knowledgable folks will chime in.
Unfortunately, I'm certainly not the guy that can give you any suggestions, but I always like seeing you guys from the "other side of the pond" showing up at our little watering hole here.
Good luck in your search, I'm sure a few knowledgable folks will chime in.
09-26-2006 | 05:42 PM
#3
Charter Member # 55
Joined: Oct 2000
Posts: 20,232
Likes: 2,482
From: Omaha/LOTO
Re: Engine height
Your propslip #'s are very good at 3-7%. The Mirage plus also has a high rake and should be able to lift the bow just fine. If they are blowing out when you trim up, then I would say to try the extra 2 inch set back that you talked about to lower them a little.
