A25 Performance

[Sunsetrider]

My A25 is a 76 with the original 36hp MD17C . We launched today, and as is the case every spring, we pray the old bugger starts up nice and quickly! This year, as every year for the past 6 years I have owned it, the trusty VP roared to life at the first twitch of the key . . . YES!
And all the way to the berthing marina, it hummed along like a champ.
Now, I think my A25 is as quick on the water as any of this ilk, but it is always nice to have a measuring stick, because the rpm/kts ratio gives one a sense (in my amateur opinion) of how well the engine, prop, and hull are working together.
On our one-hour journey today I kept the revs at a very conservative (in my way of thinking) modest 1800+ a titch, moving along at a steady 7.2 kts, per the pic below (you might have to blow the photo up to see the GPS SOG figure).
I think this is a very satisfactory performance for this elderly vessel. Cranking it up to 2200 rpm moves it along substantially quicker, but 7.2 kts is normally good for me, and the fuel efficiency is terrific at that level.
Posted for those new to the A25, or considering same. I would guess that repowered versions of the semi-displacement hull would see even better performance?

[DesertAlbin736]

That shows the difference between later De Luxe model & early full displacement hulls. The first A25s had only 21 HP 2 cyl. With our 24 HP engine we have to crank it up to 2,200 to 2,350 RPM with 2.6:1 trans gear ratio turning 16.5 X12 prop to get 6.5 knots. How's the noise level now? Didn't you mention getting some improvements from time you gave us a ride?

[Sunsetrider]

Since our ride I have replaced the insulation inside the engine box with Soundown, and had the shaft aligned and cutless bearing replaced. We can now converse at the helm without raised voices. Big improvement.

I believe that more improvement is possible by cushioning under the fuel tank and the area under the fridge cavity.

[DesertAlbin736]

That's good to hear. If not for COVID & all the related issues & closures we'd be on our way up there later this summer & pulling in to Gananoque marina after crossing east end of Lake Ontario from Oswego NY. Next year!

[Sunsetrider]

Let's see if things improve enough to have that happen.

[NickScheuer]

Our '76 Deluxe with MD17C performs about the same; 7.5 at 1800RPM. No complaint about how easily she fires up neither. Did your boat have the bumpy urethat foam noise insulation, Sunsetrider?

[Sunsetrider]

It was foam insulation but not bumpy as in spray foam - more like foam padding, just not as thick and hi-tech as the new stuff.

[NickScheuer]

Meant "bumpy" as in something appearing as it might be good for packing fresh eggs in a carton, not like "spray paint".

[Sunsetrider]

I know what you meant, NIck. Like spray foam insulation. But my OEM (if such it was) did have a foil liner on the outer facing. Just a much thinner padding c/f the new Soundown. Of course, can/t find my photos of the job.

[hetek]

I'm thinking he means "egg crate" foam, like that used on walls of recording studios and such.

Or not.

[LopezMike]

I helped build a sound recording studio once. Learned a lot.

The expert told us that heavy stuff like lead sheets on foam dealt with the low frequencies and that plugging up the last teeny hole made the difference with high frequencies. My experience quieting down my sailboat engine was that both were very important. Especially the small holes to block most of the diesel rattle.

In the recording studio the egg crate shapes helped eliminate echoes within the room. My engine does not seem to be seriously bothered by echoes.

[Sunsetrider]

I'm thinking he means "egg crate" foam, like that used on walls of recording studios and such.

Ya that sounds right. I retract,