Onan Installation

By: Ralph Hampton, July 2004
GoodNews! 37VT63

Prior System: Balmar D/C genset charging system located on platform behind stairs on starboard side. Used Yanmar 3hp diesel with direct drive 110 Amp alternator with dry exhaust thru starboard side of boat. One 8D house battery on shelf to outside starboard of generator. Two group 27 main engine and generator start batteries located next to small footprint genset. Battery banks set up as three (2 start batteries + 2 house banks of two and one 8Ds) controlled by two rotary switches.

Problems with prior system: Prior system extremely noisy. Sounded like a lawnmower inside boat. Also, genset engine blew hot air from center of cylinder head (not exhaust) and heated up engine room significantly. Efficiency at 3600 RPM of alternator was lower than rated output. Contact with Balmar indicated that RPM’s needed to be much higher via a pulley system to obtain efficiency closer to rated output.

Important Installation concerns: Measurements of genset including extra space required for exhaust elbow and other hoses; What sides of genset require access for servicing; which way to position genset; how to make room for maintaining the 3rd 8D battery in engine compartment; where to install raw water strainer; where to install wet exhaust muffler; weight and balance when moving heavy 161 pound 8D to opposite engine side + adding 350lb. genset; Whether to buy and install a remote controls panel; Maintain accessibility to engine space walkway between starboard side of engine and genset area to starboard.

New System: 5Kw Onan A/C diesel genset with sound shield. Moved the one starboard 8D battery to port side upper shelf above the other two 8D house batteries on a lower shelf on port side. Moved the two start batteries to starboard upper shelf where the one 8D was previously located. Rewired batteries so have only 2 instead of 3 house banks controlled by one switch in galley. Installed raw water strainer and hose from galley salt-water rinse seacock located just inside and slightly under entrance to engine room from galley. It was ¾” seacock with a reducer. Removed reducer. Strainer installed on a small vertical board that was attached to edge of extended sole next to edge of stairs. Is not in the way when entering and works great. Installed genset lying fore to aft on starboard platform. Placed small round 6”x6” Naqualift wet muffler behind genset and in front of shelving – it just fit. Used side inlet with top outlet. Outlet is straight up to a loop and then slopes to exit at previous exhaust on starboard side of engine room. Installed a two breaker panel with safety slider against forward bulkhead to switch from shorepower to generator power. Hooked up direct to shore power inlet on port side and back. Left relay intact for auto switching between shore power and inverter located behind main breaker panel. Hung fresh water plastic overflow tank on edge of shelf just behind stairs so easy to see and reach without removing stairs. All fuel, water and D/C start lines exit the right side of genset which is positioned just behind stairs. Decided not to go with remote controls panel since front panel genset start controls are so convenient and would need to open engine room door to open raw seacock for operation in any event as I keep seacocks closed unless in use (except galley sink).

Reasons for choosing an Onan: Comparatively lower and reasonable price ($6136 + tax) then Northern Lights and most others. One of smallest footprints for installation; Acceptable db spec of 71 compared to our old system around 95-100 db. Nice operator controls. Maintenance accessibility good except for raw water impeller. (a slight tradeoff). Small and reasonable fuel consumption. Onan is distributed by Cummins (the actual genset engine portion is a Kubota however) and since our main engine is a Cummins, I thought it would be helpful in the long run to have to only deal with one engine manufacturer + Cummins has a lot of service locations. I looked at several different units. I narrowed it down to Onan and Northern Lights. With three cyclinders, the N.Lights could run at a lower 1800 RPM instead of 2900 and so would probably be quieter. But the unit required more installation space and was more expensive.

Surprises: Decibel level ended up being 82db within one foot of unit instead of 71db. However, due to existing engine room installation, salon db level just outside closed engine room door area and galley area is 58-60 db = lower than conversation and quite acceptable. A huge improvement over prior system. Exhaust noise outside boat is slightly louder than would prefer but should be acceptable. Believe this is due to unusually short exhaust run from genset and large 2” exhaust. Also, needed to go with smallest wet exhaust available to achieve installation instruction minimum of a 12” drop of exhaust water from water mixing area of genset. The next size up raised the inlet 2.5 to 3”. In talking to muffler manufacturer, I learned size does not usually equate to bigger = quieter. During operation, there is not much water in the muffler. Larger size is needed on longer runs from engine so that discharged water after engine shutdown can be appropriately accumulated. Since our exhaust run length (different than drop) was only slightly over minimum of 12 inches at 15-18”, we seem to be able to get away with this very small 6”x6” round muffler. Positive surprise is that with built in electric fuel pump I won’t have to be concerned about air bubbles when changing fuel filter. I can just run the fuel pump without starting the genset and it will pump fuel through the system and discharge air bubbles back to the tanks via the return line.

Opinion of final results: Installer listened to my concerns and suggestions, applied his expertise and did a professional and well thought out installation job. Space requirements in all areas were met. Noise level is enjoyable. We talk and don’t notice the unit anymore. Price was affordable, relatively speaking. Unit is attractive and doesn’t consume the area. I think I will have room to add an A/C unit someday without sacrificing engine room accessibility walkway space by removing part of the shelving.

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