martynwhiteley
Active member
MerCruiser D1.7\'s RULE OK !!!
Wow,
Just got back in from my first couple of hours trying out my new single diesel installation on the Birchwood 27.
I've read amazing things about this engine on the net, and how people marvel over its capability to put the 3.0 135 hp petrol merc in the shade, despite being only rated at 120hp. But I'd resigned myself to expecting that only one of them in a 3 1/2 ton Birchwood would not lift it onto the plane. Spannerman had confirmed my expectation, however Tr' can continue to drool...!
At 1000 rpm it trundles along whisper quiete at 3 knots. 2000 rpm and the noise rises giving 6 knots. A short push forward of the control (got to be gentle whilst 'running in') and the boat was up on the plane!
Despite not having the bennet tabs recommissioned yet, and leaving the leg fully trimed in, the paddle wheel read 16.1 knots, the gps 15.9 at 4050 rpm!
I thought I was pushing my luck with a 15x15 prop, the softest easily available. Merc and Steel Dev. reckoned I'd really need a 16x12" to get the revs, but (albiet with only 3 crew and light tanks) it looks like the little 1.7 will cope with the 15".
With the two 120 BMW petrol running flat out I never saw more than 23 knots, and I bet the Merc. 1.7 will extend to at least 17 knots on a full (run-in) trial with optimum trim. The best thing being that it will now only cost about £8 per hour, not £50 per hour to push on a bit.
The bad news is low speed wander, much worse than when running on just one the two BM's. Perhaps after experimenting with trim tab positions I can reduce this (to be fair, Paul at Coastal Rides warned me that a duo-prop drive would be the best option to counter this problem, if I was going single).
I think it may be due to the Alpha drive being 'longer' from transom to prop than the BMW's. It seems logical that the longer offset would enhance the phenominum.
Still, performance beyond my wildest dreams. How sad, being exstatic over 16 knots!!!
<hr width=100% size=1><font color=blue>Oh well, maybe next weekend....</font color=blue>
Wow,
Just got back in from my first couple of hours trying out my new single diesel installation on the Birchwood 27.
I've read amazing things about this engine on the net, and how people marvel over its capability to put the 3.0 135 hp petrol merc in the shade, despite being only rated at 120hp. But I'd resigned myself to expecting that only one of them in a 3 1/2 ton Birchwood would not lift it onto the plane. Spannerman had confirmed my expectation, however Tr' can continue to drool...!
At 1000 rpm it trundles along whisper quiete at 3 knots. 2000 rpm and the noise rises giving 6 knots. A short push forward of the control (got to be gentle whilst 'running in') and the boat was up on the plane!
Despite not having the bennet tabs recommissioned yet, and leaving the leg fully trimed in, the paddle wheel read 16.1 knots, the gps 15.9 at 4050 rpm!
I thought I was pushing my luck with a 15x15 prop, the softest easily available. Merc and Steel Dev. reckoned I'd really need a 16x12" to get the revs, but (albiet with only 3 crew and light tanks) it looks like the little 1.7 will cope with the 15".
With the two 120 BMW petrol running flat out I never saw more than 23 knots, and I bet the Merc. 1.7 will extend to at least 17 knots on a full (run-in) trial with optimum trim. The best thing being that it will now only cost about £8 per hour, not £50 per hour to push on a bit.
The bad news is low speed wander, much worse than when running on just one the two BM's. Perhaps after experimenting with trim tab positions I can reduce this (to be fair, Paul at Coastal Rides warned me that a duo-prop drive would be the best option to counter this problem, if I was going single).
I think it may be due to the Alpha drive being 'longer' from transom to prop than the BMW's. It seems logical that the longer offset would enhance the phenominum.
Still, performance beyond my wildest dreams. How sad, being exstatic over 16 knots!!!
<hr width=100% size=1><font color=blue>Oh well, maybe next weekend....</font color=blue>
