Getting my Fairline Mirage onto the plane

[Sulograss]

Hi Folks

I have a 1979 Fairline Mirage with twin Volvo 140hp petrol engines. She has no adjustable trim tabs but the stern legs can be tilted although not, with the engines running.

The rev counter goes up to 6000 rpm (There is no redline) but I have only ever taken her to 3000 revs (approx 7 knots) but with the bow completely skyward and no visibilty at all.

Reading as much as I can it often appears that these boats are capable of 25 knots but try as I might I cannot get it to plane. A friends Nimbus 31 with a single diesel goes onto the plane at 6.5 knots!!

Am I doing something wrong? Can I tilt the legs prior to starting the engines to enhance the trim or is the tilt facility merely for access and cleaning? I reckon she'd also be more economical running on the plane if I can ever get it to.

Any advice or help appreciated

Tony

 

[Hummer]

Age and weight

Hi Folks

I have a 1979 Fairline Mirage with twin Volvo 140hp petrol engines. She has no adjustable trim tabs but the stern legs can be tilted although not, with the engines running.

The rev counter goes up to 6000 rpm (There is no redline) but I have only ever taken her to 3000 revs (approx 7 knots) but with the bow completely skyward and no visibilty at all.

Reading as much as I can it often appears that these boats are capable of 25 knots but try as I might I cannot get it to plane. A friends Nimbus 31 with a single diesel goes onto the plane at 6.5 knots!!

Am I doing something wrong? Can I tilt the legs prior to starting the engines to enhance the trim or is the tilt facility merely for access and cleaning? I reckon she'd also be more economical running on the plane if I can ever get it to.

Any advice or help appreciated

Tony

Will be a big factor here, she is getting on a bit and therefore the engines and equipment will be tired add to that the sheer amount of weight that you have added to it over the years will make a HUGE difference.

I was a broker in a former life and have had a lot of experience trying to get Mirages onto the plane with this set up, sometimes they do sometimes they dont.

One way to tell is to empty out absolutely everything and then try, also even with the slightest bit of stubble she wont climb over the hump.

The only ones that did without any hassle were the V8's!

Good luck.

 

[jhr]

Tilting the legs won't help you get on the plane - trim them right in. Once (or if...) you get on the plane, you can trim out a bit, which should get you a couple of extra knots at no expense.

As well as emptying her out, try putting a couple of people up front - if she's sticking her nose in the air, you are getting there, and it may just need a more equal distribution of weight to do the trick. As mentioned, a shaggy bottom will make a difference, as will barnacles on the props (out of all proportion to what you might think) so have a general clean-up underneath if you haven't done so already.

If you can get on the plane she will, indeed, be a lot more economical!

(Edit: sorry - I overlooked this bit:

the stern legs can be tilted although not, with the engines running.

. Ignore the bit about trimming the legs whilst under way. Doh!)

 

[Solitaire]

The rev counter goes up to 6000 rpm (There is no redline) but I have only ever taken her to 3000 revs (approx 7 knots) but with the bow completely skyward and no visibilty at all.

This is where your problem is! You need to use the full power to overcome the bow wave inertia. I can almost gurantee that you are also just feeding the power in up to 3,000 RPM.

A planning boat gets on the plane by using power to move the bow wave back along the hull, once you go over the "hump" then you will be planning! all you are doing at the moment is asking the hull to perform like a displacement hull and as a result the bow stick up in the air on the bow wave. Push the throttle into max mode quickly, the boat will then get on the plane and then you can throttle back to what is comfortable.

You must push the throttles forward in one easy movement not just feed the power in gently, if she does not get on the plane then there is something else wrong. As others have said, weight and dirty hull can play a part, but I'd look to your use of the throttle first.

Why have you never gone beyond 3,000 RPM is my next question? Are you in a river with a speed limit?

A friends Nimbus 31 with a single diesel goes onto the plane at 6.5 knots!!

I also question that figure as well - 12-15 knots maybe. 6.5 knots very sceptical!

 

[Sulograss]

Thanks

Thanks guys for your comments.

Yes the boat is currently on the river and restricted for speed although there are areas without the limit to try the planing excercise.

Yes, I have been feeding the power in slowly and if I think back to my water skiing days with a 14 foot Simms super V it was full power right from the offset to get the skier up and the boat on the plane so, this is a good point. The hull is cleaned and antifouled annually so not much to worry about on that score.

The 6.5 knot figure was given by the owner I haven't seen it for myself but he may apply full throttle to get on the plane and meant the boat will plane at speeds down to 6.5 knots?

Many thanks

 

[Solitaire]

Yes, I have been feeding the power in slowly and if I think back to my water skiing days with a 14 foot Simms super V it was full power right from the offset to get the skier up and the boat on the plane so, this is a good point.

Apply the same base logic and I think you will notice a difference. It may not leap out of the hole, as others have said, you won't with engines of that age be developing the original HP but you should notice a big difference.

The 6.5 knot figure was given by the owner I haven't seen it for myself but he may apply full throttle to get on the plane and meant the boat will plane at speeds down to 6.5 knots?

I still reckon it will drop off the plane at that speed even so. Anyway, not his boat we are concerned with it's yours, so try the above and let us know how you get on.

 

[GrowingLad]

Although your boat is a bit bigger than mine, I only have a single VP115.

What I would suggest is a give it a bit more revs, mine likes to go up to 4000 to get her up reasonably quickly and sit around the 3600 mark quite comforatably on the plane.

The saving grace is adjustable tabs, makes life a lot easier that's for sure.

 

[jimg]

Thanks guys for your comments.


The 6.5 knot figure was given by the owner I haven't seen it for myself but he may apply full throttle to get on the plane and meant the boat will plane at speeds down to 6.5 knots?

Many thanks

I am pretty sure the NImbus 31 is a semi-displacement hull, so he is not "planing" as such.

Oh, I see that the Mirage is semi-displacement as well!

 

[oceanfroggie]

I am pretty sure the NImbus 31 is a semi-displacement hull, so he is not "planing" as such.

Oh, I see that the Mirage is semi-displacement as well!

Agree, there is no way she is planing at only 6.5kt on a 31ft hull.

 

[Solitaire]

I am pretty sure the NImbus 31 is a semi-displacement hull, so he is not "planing" as such.

Oh, I see that the Mirage is semi-displacement as well!

Good point - but even so she should rev beyond 3000. Our Storebro 31 is semi displacement and cruises comfortably at 18 knots. But she does need wellie to get her up. We run AD41B's through hydraulic gearboxes on a 5 bladed prop configuration and at 3,000 rpm she is happily chugging along at cruising speed. But at 6 knots she is running displacement!

I just checked out details on Mirage - http://www.boatsforsale-uk.co.uk/archive_boat.php?boat_id=28

 

[PCUK]

You may find it helpful in the long run to fit manually adjustable trim tabs. Set them up to get onto the plane and leave them alone as they will have no effect at displacement speed. About £50 and a days work could make all the difference!

 

[Divemaster1]

In 1979 these were delivered with 270 and 280 drives. None of which had hydraulic rams for other than lifting the drive unit... not for trimming under load. Initial trim would be done much like an outboard at the time, which meant lift the leg out of the water, and move the bolt on the transom plate out, or in... In your situation, he bolt should be in the last hole, closest to the stern of the boat, for getting the boat on to the bow wve (plane) at as low speed as possible. After you achieve this, you can play with the trim bolt.... the further out the bolt is, the slower she'll get up, but as hull is lifted higher out of the water there will be less friction and thus higher speed....... all a trial and error.

With potential "tired" 140 petrol's onboard, I'd dare to say that you may struggle to see 24 knots though..

 

[Rum_Pirate]

You do this

and you want to do this

1. Is your hull clean?

2. Are the props the right size? Too long a pitch could mean that your engines can provide enough power to get on the plane due to slip.

3 Are the props the right size? Too short a pitch could mean that your engines race too high before boat is able to get on the plane.

4. Is the boat filled with non essential items, and too much weight eg a VERY long anchor chain.

5. Is boat trimmed properly? Too much weight in the stern could prevent the boat getting on the plane.

6. Are engines trimmed properly? Try trimming them right in (ie keep the bow down).

Suggestion, clean bottom, push throttles to the stops (only for a few seconds say 15), IF you get on the plane throttle back to the speed just before the boat comes off the plane. This will take some practise.

My 22'0" centre console Mako

with two 85hp Yamaha outboards with 8 people aboard and 30 gallons of fuel (about200lbs) needs approx 4500 - 5000 revs for a few seconds (about 5) then cruises at a good speed when throttled back to +/-3,000 revs.
It does have the benefit of electronic engine tilt trim.
It does not have trim tabs on the boat and no longer have doelfins on the engine cavitation plates.

 

[ms1]

I have a Mirage
Divemaster is right DO NOT attempt to trim the legs using the electric power leg lift.
Clean bottom helps.
Full water tank helps (ie weight in the bow)
You need the right props (likely 15 x 17). Prev owner may have down rated the props for river running even so you will get nowhere with 3,000 revs. Full power then throttle back as already suggested. Comfortable plane will be up around 14 knots something like that .

After around 6.5 to 7 kts (ie displacement speed) you just start pushing a wall of water in front of you (using fuel) and building yourself a nice hump.

Without trim tabs you will be nose up quite dramatically until you get over the hump. Even with trim tabs it's not much better. At around 20 kts plus, tabs will just slow you down anyway.

These are still quite fast boats if your engines have been cared for.

I have 4 x 25 kgs bags of sand in the bow to aid attitude in the water as I re-engined with diesels which are heavier.

 

[plesbit]

Trim tabs

Get yourself a decent set of adjustable trim tabs. Without them Mirages tend to bury themselves at the back end and when that happens you'll need real power to climb over the hump. 30 year old 4 cylinder petrols are not exactly "real power". A loaded Mirage weighs the best part of 5 tons so that's a lot of boat to push over the hump.

For 2.5 years I had a Mirage with twin AQD32A's. That's 106hp per side, so a fair bit less than yours, and the engines were nearly half a ton each, probably about double the weight of yours. They were even older too! But even without trim tabs she'd do 10-12kts, though the riding angle was virtually unusable. With tabs she'd settle out at 12-14kts and cruise comfortably. With low fuel and water she'd get out properly and do 16-17kts when trimmed properly though you'd be getting pretty close to the governors at that speed.

Older, heavier, far less power, but still outperforming yours by some distance. But without hydraulic trim tabs, forget it.

I think your engines may also be delivering a long way short of their stated power if 7kts is all you can manage. Either that or I just got better out of the diesels (without the tabs) because they are higher torque and lower revving engines. Any engine only delivers its stated power at maximum revs. My old diesels could pull 3400rpm out of their maximum 4000rpm even with no tabs (though the riding angle made you basically blind) but your 4 cylinder petrol jobbies are pulling 3000rpm out of 6000rpm - far further down in their rev range and I somehow doubt that suits their torque curve.

 

[tinkicker0]

Agree. 3000RPM at 7 knots sounds like a lot of revs for not a lot of speed.

I get 7 knots at 1500 RPM.

 

[powerskipper]

mm

Hi Folks

I have a 1979 Fairline Mirage with twin Volvo 140hp petrol engines. She has no adjustable trim tabs but the stern legs can be tilted although not, with the engines running.

The rev counter goes up to 6000 rpm (There is no redline) but I have only ever taken her to 3000 revs (approx 7 knots) but with the bow completely skyward and no visibilty at all.

Reading as much as I can it often appears that these boats are capable of 25 knots but try as I might I cannot get it to plane. A friends Nimbus 31 with a single diesel goes onto the plane at 6.5 knots!!

Am I doing something wrong? Can I tilt the legs prior to starting the engines to enhance the trim or is the tilt facility merely for access and cleaning? I reckon she'd also be more economical running on the plane if I can ever get it to.

Any advice or help appreciated

Tony

I thought you were trying to get it on an airplane. I sat thinking about it and then thought, got to find out why????


I had been talking to someone about flying and was mind set, did give me a giggle for a min, so thanks.