Trimaran - Especially Searunner - Owners

[owly]

A really really crude sketch

[Buzzman]

Interesting idea.

Cuppla points.

1. The exhaust from the Honda motor would need to be routed outboard to prevent npoise, fumes and CO (carbon monoxide) from building up in the engine compartment or cockpit

2. You might like to consider a British Seagull lower leg for the 90deg turn in the shaft. They are low geared, feature bronze bushes rather than the more fragile steel bearings and are designed to run at relatively low revs (not more than 4000 rpms). If that suits the power characteristics and revs of the Honda it might be a good fit.

Remember that the very first multihull to circumnavigate in the modern era, David Lewis' Prout's-built Rehu Moana, used a 5HP British Seagull 102-series as its sole auxiliary propulsion.

[rossad]

owly how bout going electric. Good for 2 hours motoring. I nearly considered electric for my 37SR. It was touch or go but in the end what changed my mind was the new Yanmar 30 and its latest technologies. I can motor some serious distances now which is great for when approaching a country when 100 miles out... situation with no wind and a serious front is coming in 24 hours... like NZ. this happens all the time.

[owly]

Originally Posted by Buzzman

Interesting idea.

Cuppla points.

1. The exhaust from the Honda motor would need to be routed outboard to prevent npoise, fumes and CO (carbon monoxide) from building up in the engine compartment or cockpit

2. You might like to consider a British Seagull lower leg for the 90deg turn in the shaft. They are low geared, feature bronze bushes rather than the more fragile steel bearings and are designed to run at relatively low revs (not more than 4000 rpms). If that suits the power characteristics and revs of the Honda it might be a good fit.

Remember that the very first multihull to circumnavigate in the modern era, David Lewis' Prout's-built Rehu Moana, used a 5HP British Seagull 102-series as its sole auxiliary propulsion.

As I was doing that extremely crude sketch using Gimp........ which I have problems with making it do what I want, I came up with a couple of possible solutions. At the foot of the quarter berth there is a space which is a storage area for the galley, and is in the wing. The exhaust pipe would be routed into that area, where it would pass through a vertical muffler, probably custom made, and then make a sharp downward bend and go down and exit under the wing.... the area of course would be just at the forward end of this compartment and would be well heat shielded from the rest of the storage area. The intake would draw through this same compartment via a filter in the divider. By drawing air here, if there were any exhaust leakage it would be sucked into the intake. The negative pressure created by the air filter would ensure this. The vertical loop up through the muffler and then down to the exit in the underwing would greatly reduce any chance of getting a gulp of seawater. A simple valve could provide added insurance. Thanks for the seagull idea...... the Honda is a 3600 RPM motor, though I would rather be able to use Evenrude, Mercury, or even Honda parts. It inevitably will end up calling for some prop experimenting, and ideally a folding prop, so how many options are there? If it's not obvious to anybody, this rude sketch is a view from the starboard side, but the engine is on the port side. I should probably have flipped it. It should also be noted that the engine is not quite to scale, it's actually larger, by perhaps 20%, which means that it would stick up through the cockpit grate, and it probably should have a weather cover of sufficient strength to step on without damage. The whole idea is a bit "off the wall" at first glance, but on consideration you will see that it meets a number of worthwhile objectives. First it gets the prop where it should be.. under the boat... Second it uses a cheap, rugged reliable, and very available engine. Third it places the engine in a very serviceable location, and at 90 pounds it is fairly easy to remove. It would be attached to the shaft with a coupler that was easy to lift out of. Disconnect the exhaust, and intake, and throttle linkage, and lift. If you cant lift 90 lbs, the boom is right there to help. And last, it completely eliminates sea water cooling, which I've always strongly objected to. Cooling air would be drawn from beneath the cockpit grate, and heated cooling air exhausted straight upward into the cockpit. It's not as if the idea was to run the engine for many hours or days at a time, it's for brief operation when entering and maneuvering in a harbor, making a passage through a narrow break in a reef in the Taumotos &c. With this engine, keeping a full stock of parts would not entail a lot of expense or weight. A complete Honda carb, a few sparkplugs, a spare cdi..... All pretty trivial and easily replaced pieces. Outboard lower units of small size can be had on Ebay for a few hundred dollars, and of course that is the critical component... gears, bearings, etc. Connecting to the shafts is pretty easy stuff... at least not "rocket science", and well within my experience and expertise. H.W.

[Mark Johnson]

Originally Posted by rossad

owly how bout going electric. Good for 2 hours motoring. I nearly considered electric for my 37SR. It was touch or go but in the end what changed my mind was the new Yanmar 30 and its latest technologies. I can motor some serious distances now which is great for when approaching a country when 100 miles out... situation with no wind and a serious front is coming in 24 hours... like NZ. this happens all the time.

It seems to me that one would either want ALL of the advantages of a proper diesel installation, like several days of motoring ability, even on 10' waves, with power, twice the mpg, and 30 year reliability... OR, the considerable option of the sled, with less ability, less fuel efficiency and lifespan, but a HUGE plus... it is easier, cheaper up front, and:

Barnacles absolutely LOVE underwater metal, which you can eliminate entirely with the sled and OB, which can be pulled up, clear of the water. For service, you can take the motor to the shop, saving 500%!

Also... 90% of the difficulty of any inboard installation is installing the shaft log, shaft, and strut, all of which must be aligned PERFECTLY.

Sea water flowing through the engine is not an issue with a fresh water cooled diesel. Mine is 21 years old, and in excellent shape.

Otherwise, it is not an issue with an ob motor that you flush regularly, as long as you are OK with half the lifespan.

An air cooled gasoline engine as drawn, would likely run hot, due to being enclosed, and LOUD, due to having dry exhaust.

It is a clever idea, but I would either go more expensive (up front) with a proper small diesel, OR go easier to install and cheaper, with the sled.

On a boat this size, they work quite well UNTILL the seas get rough, and sometimes I really wish I had NO underwater metal, like every 4 weeks in sailing season, when scraping hard growth off of the drivetrain.

[owly]

Originally Posted by rossad

owly how bout going electric. Good for 2 hours motoring. I nearly considered electric for my 37SR. It was touch or go but in the end what changed my mind was the new Yanmar 30 and its latest technologies. I can motor some serious distances now which is great for when approaching a country when 100 miles out... situation with no wind and a serious front is coming in 24 hours... like NZ. this happens all the time.

......... Batteries. I'm not convinced that batteries within the size and weight range that make sense exist, and of course they need to be charged. 2 hours of operation at 5 HP output requires 7.5 KWH of battery storage approximately. Batteries are heavy and expensive, and relatively short life. H.W.

[owly]

Originally Posted by Mark Johnson

It seems to me that one would either want ALL of the advantages of a proper diesel installation, like several days of motoring ability, even on 10' waves, with power, twice the mpg, and 30 year reliability... OR, the considerable option of the sled, with less ability, less fuel efficiency and lifespan, but a HUGE plus... it is easier, cheaper up front, and:

Barnacles absolutely LOVE underwater metal, which you can eliminate entirely with the sled and OB, which can be pulled up, clear of the water. For service, you can take the motor to the shop, saving 500%!

Also... 90% of the difficulty of any inboard installation is installing the shaft log, shaft, and strut, all of which must be aligned PERFECTLY.

Sea water flowing through the engine is not an issue with a fresh water cooled diesel. Mine is 21 years old, and in excellent shape.

Otherwise, it is not an issue with an ob motor that you flush regularly, as long as you are OK with half the lifespan.

An air cooled gasoline engine as drawn, would likely run hot, due to being enclosed, and LOUD, due to having dry exhaust.

It is a clever idea, but I would either go more expensive (up front) with a proper small diesel, OR go easier to install and cheaper, with the sled.

On a boat this size, they work quite well UNTILL the seas get rough, and sometimes I really wish I had NO underwater metal, like every 4 weeks in sailing season, when scraping hard growth off of the drivetrain.

Everything you say is true.........except the statement about running hot. The entire area beneath the cockpit grate is the cool air source for the engine, and the hot air is exhausted straight up.......... The 31 is highly limited in engine weight, so a diesel is pretty much out of the question. I too dislike having any metal in salt water. H.W.

[Mark Johnson]

Originally Posted by owly

Everything you say is true.........except the statement about running hot. The entire area beneath the cockpit grate is the cool air source for the engine, and the hot air is exhausted straight up.......... The 31 is highly limited in engine weight, so a diesel is pretty much out of the question. I too dislike having any metal in salt water. H.W.

The engine itself, is gasoline, and an ignition potential in the same compartment with gasoline. This is inherently less safe than using diesel. If you are dead set on this installation, perhaps a small Diesel engine?

On the sled... it has a deep V nacelle, that really cuts down on the pounding, and should be about a knot faster when pulled up, than any installation with a shaft and folding prop.

Remember, Searunners numbered close to 3,000, over about 45 or 50 years. They are among the most thought out and highly developed boats in the world, so a better mousetrap is rare.

Also... being so "compartmentalized", they really do not lend themselves to changes in what goes where, beyond what I have done, in moving the Diesel engine to the spot below the aft companionway ladder. This was John's idea!

If the plan is to "express yourself" and you are OK with taking a big risk... then it makes sense for that reason.

My three boat projects took 21 years altogether. I would not have done it without pretty much following the plans, because I would not want to gamble with many years of effort and money.

Contact John Marple's for another opinion. I did not finish my engineering degree, but he did, and he has the feedback from thousands of SR owners. [emoji1365]

Best of luck with it...
Mark

[Cavalier MK2]

I looked at air cooled 4 strokes for similar reasons but tended to think of retractable longshaft/longtale installations to keep the outboard benefits. In reality I found little expense in going through used outboard engines. On the Nicol the different hull shape did a good job of keeping the prop in the water but this year I went the sled route. Different structure meant I got to design it as a consolation prize but it follows the v bottom route. There were some benefits I didn't expect.

Less vibration as the long arms and hinge attachment reduce the vibration transfer to the boat.

Less noise as the power head is running surrounded by the wing instead of behind the aft cabin hatch.

It is safer if there ever is a fire as cutting the safety line would let it submerge.

The convenience is great for operation and there is enough range of retraction that I don't have to kick it up/tilt.

A sled has some possibilities for what you are doing but the same challenge. Taking the salt mist out of the air cooling air. It has to be high up enough and/or baffled/filtered or you will still have corrosion problems. The air fan may surprise you with the amount of air volume you need to be able to supply so look into it. I remember the surprise at how much air flowed around a VW bus engine to cool it plus you have to supply the intake for the fuel system.

[owly]

I'll reiterate the point that there is no diesel available that is suitable for the SR331.... It's a weight issue. The point about fuel and an engine in the same space is not much of an issue at all with the type of ignition system used on the honda engine. The CDI ignition incorporates the spark plug wire right on the coil as a unit forming an extremely short tight fitting system, with none of the long loopy wires, magneto, etc, or a typical marine gas engine such as the Atomic twin. The chance of producing an external spark is almost nil. The electric starter if used has a high potential for igniting fuel vapors. It should also be pointed out that an inboard as shown in Jim's drawing, in a tight space, has a fairly high probability of fuel leakage from hoses, fuel pump, or flooding of the carburetor. It's far from a "safe" environment, nor is it easy to get into to service and inspect. Spilled fuel beneath the cockpit grate has no place to go except by evaporation. Fuel floats, so if it runs down the centerboard trunk, it will stay there. The best location for carrying fuel in an open wing SR31 would be between the struts. There really is no "safe" gas engine installation on a boat so long as gas must be carried separate from the tank on an outboard...... which it must. An outboard on a sled.... however you define "sled" may be the best solution. I don't like the transom mounted outboard for a number of reasons, which I need no enumerate here. I have of course as I stated before a huge objection to salt water running through any part of any engine. It's been said that one should give it a fresh water flush....... Which is entirely impractical at sea where you can carry only limited amounts of fresh water........ and of course how do you flush it??? Do you hook a hose up and pump it through? How much water is needed for a decent flush? Suppose I'm leaving Nuku Hiva, and using the motor to get out of the harbor. Do I have to carry an extra 20 gallons of fresh water and a pump of some sort? Lower it into a drum of fresh water and run it? I don't think flushing is a realistic option except for the weekender. Below....... If I can get them to come through are two photos. One of an SR31 with a sort of "sled", and the other showing the rear strut assembly on another open wing SR31. The question in the second photo is where do you put the "sled"?
What it all boils down to is that there are no easy answers...

H.W.

[Mr Big]

My Searunner 37 is for sale in San Diego:

For Sale: SeaRunner 37 Trimaran San Diego - Cruisers & Sailing Forums

[md7a]

Owly - Interesting idea with the air-cooled honda and right-angle rig below. On my A-frame SR31 there's about 10" of clearance between the cockpit subfloor and the framing under the forward quarter berths; about 12" to the underside of the cockpit sole panels (no grate on my boat, just panels with holes). That's not much space, but if the honda will fit, there might be side benefits for the boat: that sub-cockpit area is nasty, wet and anything in there tends to rot; some heat and air movement might improve the climate. Your exhaust could go right through the hull and come out below the wing. I don't sail in big water, but I've never known waves to slap under the wings, so your exhaust would be somewhat protected.
That being said, I'll share that I'm thinking about repowering my boat, which has the standard transom-hung outboard on a slide, and Cavalier's comments about the advantages of a sled sound very persuasive.
The "sled" in your A-frame pictures would mount under the wing and the motor head would come up well abaft and inboard of the a-frame attachment points, including the transverse wood plank. It would be out of sight at the top right of the a-frame photo.

[md7a]

Thanks to a lot of help from John Prentice I was able to replace the centerboard on Pineapple Express (SR31 #105).
I posted some photos in an album, and shared with the Searunner group.

This was a pretty standard board, built mostly to plans, but a little thin and without the split hose padding -- the original builder made the boat's centerboard trunk narrower than plans, so the old board was always a tight fit.
Here's the remove-build- replace sequence:

Old board stuck in trunk


Old board cut out in pieces


New board shaped to plans



New board with 'glass and epoxy


centerboard pin receiver tube / extension (for replacing pin with boat in the water)

[owly]

Originally Posted by md7a

Owly - Interesting idea with the air-cooled honda and right-angle rig below. On my A-frame SR31 there's about 10" of clearance between the cockpit subfloor and the framing under the forward quarter berths; about 12" to the underside of the cockpit sole panels (no grate on my boat, just panels with holes). That's not much space, but if the honda will fit, there might be side benefits for the boat: that sub-cockpit area is nasty, wet and anything in there tends to rot; some heat and air movement might improve the climate. Your exhaust could go right through the hull and come out below the wing. I don't sail in big water, but I've never known waves to slap under the wings, so your exhaust would be somewhat protected.
That being said, I'll share that I'm thinking about repowering my boat, which has the standard transom-hung outboard on a slide, and Cavalier's comments about the advantages of a sled sound very persuasive.
The "sled" in your A-frame pictures would mount under the wing and the motor head would come up well abaft and inboard of the a-frame attachment points, including the transverse wood plank. It would be out of sight at the top right of the a-frame photo.

The top of the engine might stick 4" above the cockpit floor. The Honda specification is 15.9" tall, but that may include the length of the output shaft, which is a bit over 3" long, and ideally would project down through into the compartment below where the engine is supposed to be. A smooth hump sticking up 4" through the cockpit sole as an engine cover would not be a huge inconvenience. One would definitely want to make sure there was plenty of ventilation from below for cooling. I was backward on my airflow..... The Honda sucks from around the pull rope, and exhausts hot air below, from around the head and cylinder shrouding. This would blow hot air into the compartment beneath the cockpit sole........ a good thing.
Note the attached drawing for this engine. The only vertical dimension shown is 10.79 inches, from the mounting base to the lower edge of the recoil starter assembly, which is probably an additional 2 inches or a bit more. That suggests that the shaft length is included in the 15.9" total height, which means that the necessary hump in the cockpit sole would only be a little over an inch. This would probably be a removable cover which you would lift off when the engine was running. A rubber seal around the cooling inlet area and the bottom of the cockpit sole would be desirable so it would draw only cool air from above.
The exhaust as you say, could go straight through the side of the boat under the wing, but I'd rather make the hump up through a nice quiet muffler, and back down vertically through the wing just aft of the quarter berth. That method offers greater protection from seawater........ it only takes one good gulp to create headaches drying an engine out. Also drawing air in from the sterncastle for the carb, does create a safety factor against exhaust leaks. It's the way I would approach it........... but everybody has to do things their own way. Your dimensions make this look like a very doable system. Also below should be an image of a Suzuki 9.9 HP lower unit. Driveshaft length shown is 14", which gives an idea of overall dimensions. $179 on Ebay. Obviously one can do what one wants with the driveshaft. With that small horsepower a heat shrunk drive hub of some sort would do the job, or the shaft could be keyed and pressed on.

H.W.

[Cavalier MK2]

Good sequence on the centerboard Will. One of the other benefits of the sled for me was moving the outboard weight forward off the transom. It is further forward than the set up on a Searunner 31 but you'd still get a little improvement there as well as less cavitation in waves than the transom installation.