Oscar Gelpi
My old Perkins engines started petering out a few years ago. My last three summer cruises (one to the FL Keys and two to the Abacos) were spent cruising at about 8 knots as the engines didn’t have enough HP to get the boat up on plane. The boat originally cruised at approximately 12 knots at 2150 rpms and topped out at roughly 15 knots at 2400 rpms. The engines were only rated at 185 HP when new in 1978, no telling what they were putting out the last few years.
I had asked my mechanic to keep an eye out for good pair of used engines to re-power with as I didn’t have the funds for new engines nor did I want to put a lot of money into rebuilding the old engines which I felt were barely adequate even in their prime. He finally came through with a pair of 1994 300 HP Cummins 6BTA. That was a lot more horsepower than I was looking for or needed but the deal was too good to pass up.
I had considered and rejected several options including the V-8 Cats. The six cylinder B series seem to be tailor made for this boat. The engines actually weigh about 300 lbs less (each) than the old Perkins and the height was a bit lower. A lot of the weight savings came from losing the huge cast iron after-cooler on the Perkins. Overall the dimensions were very close to the Perkins.
This project was going to have to be done on a shoestring so we did some wheeling and dealing. The old Velvet Drive transmissions got traded for some instruments and spare parts and the engines themselves were traded for a pair of rebuilt ZF220 gears. The first order of business (once the old engines were out) was to
fabricate welded aluminum covers for the engine stringers. The stringers
had a cutout near the back to accommodate the inclined Perkins. Next he
installed new supports for the gears and bolted the ZFs in.
ZF Transmission mounts on rails
While the engines were out I took the opportunity to replace the rotted and
oil soaked boards (3/4" plywood) between and flanking the engines. I put on
several coats of varnish on the new boards (top of picture) before they were
installed. The boards outboard of the engines go over several stringers. Water
(stagnant and putrid) had accumulated in the compartments between the stringers
as there were no weep holes through the stringers to allow it to drain. A little drilling and
some epoxy on a Q-tip fixed that. I also cleaned out an extraordinary amount
of caked up grease and oil. For this job I don’t know of anything better than Roll-off.
New plywood board outboard of engine bed
The new engines required upgrading the exhaust from 4" to 5" and the water intake to 2". The old elbows were copper and had rotted through in a few places. The new ones are fiberglass and should hold up better.
New 5" exhaust w/ fiberglass elbows
Cummins recommends upgrading the Racor from the 500 series to the 900 but we stayed with the smaller Racor and everything works fine so far. We did however re-position the filters. They were previously mounted in the generator compartment space forward of the engines. This meant that filter changes were done lying on my belly hanging into the compartment! The new spot is on a newly fabricated mounts in the center hatch between the engines.
Racor mounted on new aluminum bracket
The old shafts had to be replaced as they were a bit short. The original shafts were 1 1/4" and I really wanted to stay with that size so as not to incur the added expense of changing struts and what not. Some posters on Diesel.com felt the engines needed 1 ½" or even 1 3/4" but the shaft calculator didn’t bear that out and the mechanic felt that as long as I wasn’t slamming the engines around or doing shotgun starts that I would be fine. We went with 1 1/4" Aquamet 22s.They were $850 for a pair of 89" shaft and they have worked out fine so far.
The props were another story. The original 19x20 props only wound the engines up to about 2400 RPMs. A pair of 19x18 3 bladed props got the engines up to their rated 3000 RPMs.
The old tachs were incompatible with the new engines so they were replaced with VDO mechanical w/built in hourmeter. I also replaced the temp gauges while I was at it. Fuel lines were upgraded to ½" supply and 3/8" return.
As I said before the engines were a nice fit in the spot vacated by the old Perkins
Note position of filter
I also replaced the fuel manifold by swapping out the troublesome gate valves with positive shutoff ball valves. I also replaced the two gate valves at the fuel tank the same way.
Fuel manifold
Another upgrade was adding an Oil X-Changer unit plumbed into the engine and transmission. The unit is mounted in the center cockpit compartment between the deck supports. This puts it right behind the engines and transmissions, easily accessible but still out of the way. I screwed another piece of varnished board in front of it as added protection from anything in the compartment that might slide around.
Cruise 12@2150 19@2400
Fuel 6gph? 15 gph per engine, fully loaded boat
Top end 15@2400 25@3000
Weight 1500+lbs 1280lbs
Shafts 1 1/4" 1 1/4" Aquamet 22
Props 19x20 3 blade Dynajets 19x18 3 blade Dynajets
Water intake 1 1/4" Groco SV 2" Groco Ball Valve
Exhaust 4" 5"
Filter Racor 500 Racor 500
Figuring the fuel consumption is problematic because I never top off after a long run at a constant RPM except when we’re cruising. When we’re cruising that means fully loaded with fuel, water, full coolers, clothes, dive tanks, dinghy on the bow, outboard on the stern, people, food, beer! It also means we’re usually getting 2-3 foot seas on the quarter for most of the crossing, so obviously consumption will vary depending on conditions.
The change in engines also changed the attitude of the boat as it sits in the water. First she seems to ride a little higher, just a couple of inches. I used to get a slight bow rise while on plane. No longer. The bow stays down now and I never use the trim tabs to compensate. I think that may be a function of losing those massive iron after-coolers on the Perkins. Not only were the Perkins heavier but they seemed to be weighted more at the back end.
I’m not sure that this change in attitude is all positive as it seems more of the boat stays in the water and perhaps increasing drag. However this is a completely unscientific observation on my part and may be completely wrong.
All in all I’m very satisfied with the re-power and I don’t think I’d change a thing. Please feel free to e-mail me any questions.
Oscar Gelpi