Trimaran - Especially Searunner - Owners

[sea dragon]

I've installed a 25 hp 4 stroke Yamaha high thrust on my SR 40.
It has the gearbox of a 40 hp motor and turns a 12 inch prop
Mounted on the stern on a IMC Easylift hydraulic motor bracket.
Completly out of the water at the push of a button.
So far, I haven't noticed the heavier motor causing any more cavitation problems than a lighter motor
I absolutely love it!
Finally the boat has plenty of power

[blewett_john]

Originally Posted by Boatguy30

John-

That certainly is a different approach! SR 40 Jade did a 3,000 mile Caribbean circuit last winter with a 2 Y/o 9.9 (4 stroke)hp transom hung outboard and whip staff steering!

2 stroke is useful as a backup engine but 4 is WAY better for main propulsion and quiet efficiency.

Run a Yamaha 8 and 5 hp 2 stroke on my 11,000 lb 34 cat.

I like two strokes, very simple. Plus, I can't afford two new four strokes. If I had tons of money I would have a Chris White Hammerhead 54, but with an aft cockpit (I don't like the aft cabin)

[Cadence]

Originally Posted by sea dragon

I've installed a 25 hp 4 stroke Yamaha high thrust on my SR 40.
It has the gearbox of a 40 hp motor and turns a 12 inch prop
Mounted on the stern on a IMC Easylift hydraulic motor bracket.
Completly out of the water at the push of a button.
So far, I haven't noticed the heavier motor causing any more cavitation problems than a lighter motor
I absolutely love it!
Finally the boat has plenty of power

Can you get her to plane? Seems like a lot of weight aft?

[PhantomBoatwork]

Originally Posted by w32honu

Phantom,

Curious what your choice and solution for water tanks was? Material? And location of install?

I think it is nice to leave the bilge free of "stuff." But it is nice to have that amount of weight as low as possible. Just curious........??

Same goes for fuel tank. Maybe a slightly smaller tank installed under a cockpit seat. Easily accessed and gravity feed (a lot less suction feed anyway) for the motor. But again the weight problem.......??

Just thinking ahead and trying to plan. Want to avoid the "shoulda, woulda, coulda."

Thanks in advance. Awesome job by the way. And thanks for posting the pics and the blog. I have been curious about the net install..........size of PVC and how to cut the notches....etc. Very helpful.

I got the water tanks from the tank depot. They are all rotary molded polyethylene and very stout. I measured each of the available bilge spaces and ordered the one closest to the size, and voila! water tanks. Small glitch? I neglected to take into account the steering cables in the bilge under the galley, so the aft tank had to be relocated to the starboard side of the centerboard trunk. The diesel tanks are there, as well. I was planning to have the fuel tanks custom welded by a local tank fabricator when I found tanks of more than enough capacity for about 1/4 of the cost- also polyethylene and from tank depot. Still have to route the fill piping to the decks and the vents, but the tanks are all installed and pretty much in their final position- work in progress

[sea dragon]

Originally Posted by Cadence

Can you get her to plane? Seems like a lot of weight aft?

Hi Cadence
Well,it's 100 lbs or so heavier than a 9.9hp.4 stroke
So equivilant to a 9 year old child standing on the transom.
And that is on a big, wide, forty foot boat.
The boat is designed to carry the weight of a big deisel and fuel + water tanks in the aft cabin bilge.
In my boat the bilges and stern compartment are empty.
I have a tremendous amount of reserve bouyancy.
Regarding cavitation issues,the main problems occur when the stern rises.
In this regard the heavier motor actually makes it rise less.
The bottom of the cycle isn't really much different because of all the reserve bouyancy and long waterline of my boat.
100 lbs just isn't a big deal.
My boat is very lightly loaded
I think a shorter boat would have more tendency to hobby horse.
Not a problem for me.
Weight aside,
The difference between a 9.9 and a 25 high thrust is 2 1/2 times the power.
It really makes a Quantum difference when motoring into wind,& tide.
You can motor at hull speed with the 25 when the 9.9 would be slowed to a crawl.
The hydraulic bracket makes raising the motor completly out of the water simple.
I have used them both on my boat and I'm liking on the bigger engine allot.

[Cadence]

Originally Posted by sea dragon

Hi Cadence
Well,it's 100 lbs or so heavier than a 9.9hp.4 stroke
So equivilant to a 9 year old child standing on the transom.
And that is on a big, wide, forty foot boat.
The boat is designed to carry the weight of a big deisel and fuel + water tanks in the aft cabin bilge.
In my boat the bilges and stern compartment are empty.
I have a tremendous amount of reserve bouyancy.
Regarding cavitation issues,the main problems occur when the stern rises.
In this regard the heavier motor actually makes it rise less.
The bottom of the cycle isn't really much different because of all the reserve bouyancy and long waterline of my boat.
100 lbs just isn't a big deal.
My boat is very lightly loaded
I think a shorter boat would have more tendency to hobby horse.
Not a problem for me.
Weight aside,
The difference between a 9.9 and a 25 high thrust is 2 1/2 times the power.
It really makes a Quantum difference when motoring into wind,& tide.
You can motor at hull speed with the 25 when the 9.9 would be slowed to a crawl.
The hydraulic bracket makes raising the motor completly out of the water simple.
I have used them both on my boat and I'm liking on the bigger engine allot.

Sounds like a nice setup. If the hydraulic lifts keep the engines vertical it sounds as though changing the foot oil should be a breeze while afloat.

[Cavalier MK2]

Keep in mind the windage and weight of a SR 40 compared to a 31. On a 40 if using 9.9s you'd want 2. Our Nicol probably compares to a SR34 in terms of weight and windage and a 9.9 HT is plenty. Going into a 20 knot Straight of Georgia big, steep, close chop it will still go 5 1/4 knots at cruising throttle but I have to slalom around the biggest waves to avoid the occasional hop.

[w32honu]

Originally Posted by PhantomBoatwork

I got the water tanks from the tank depot. They are all rotary molded polyethylene and very stout. I measured each of the available bilge spaces and ordered the one closest to the size, and voila! water tanks. Small glitch? I neglected to take into account the steering cables in the bilge under the galley, so the aft tank had to be relocated to the starboard side of the centerboard trunk. The diesel tanks are there, as well. I was planning to have the fuel tanks custom welded by a local tank fabricator when I found tanks of more than enough capacity for about 1/4 of the cost- also polyethylene and from tank depot. Still have to route the fill piping to the decks and the vents, but the tanks are all installed and pretty much in their final position- work in progress

Thanks Phantom,

Been out of the loop for awhile and just saw this post. Again very helpful.

We have been full time on our build. One ama is assembled and another is ready with the two sides ready to join. Currently splicing together the Vakka panels. Slinging lots of glue these days.

Thanks again.........

Cheers.

Also wanted to put out there...... Marples F-6 mold available for anyone that is interested. It is in great shape and ready to go. Free and for the taking. York, Maine US.

[snort]

When it comes time, I've pretty much decided to buy a new 6hp Tohatsu for my 31 SR. Going with "lighter" is better, if it's just enough to push the boat in most conditions.

[Cadence]

Originally Posted by snort

When it comes time, I've pretty much decided to buy a new 6hp Tohatsu for my 31 SR. Going with "lighter" is better, if it's just enough to push the boat in most conditions.

I believe you will find you are under powered. I couldn't assess the 9.9, I bought on a 31 SR with, since it was shot. .I put a 15 Honda four stroke on and was please sound wise and fuel consumption wise 7.5kns at .75 gal and about 2/3 throttle. I think that is hull speed under power. Under sail they will fly.

[snort]

Thanks for sharing your experience, Cadence.
I guess I could give it a shot, and then trade up to the 9.9.
I do notice how weight sensitive the 31 is, and, if I can get away with lighter (especially off the stern), I think the boat will sail better.
I remember seeing a comparison of a 6 hp vs. a 9.9 on youtube, and the difference was negligible in performance.

[Cadence]

Originally Posted by snort

Thanks for sharing your experience, Cadence.
I guess I could give it a shot, and then trade up to the 9.9.
I do notice how weight sensitive the 31 is, and, if I can get away with lighter (especially off the stern), I think the boat will sail better.
I remember seeing a comparison of a 6 hp vs. a 9.9 on youtube, and the difference was negligible in performance.

I had that Honda with a 28" leg hanging on the stern, The boat came with 4 six volts under the rear bunk. I didn't pull them out but added an 8D since I wasn't home yet and the 6Vs were shot. No adverse effect on trim. For what it might or might not be worth.

[Capt.Timbo]

We have a 40ft SR with a 60 HP Yamaha that is mounted aft of the sterncastle, behind the firewall. It is mounted to the deck and our gear housing unit (foot) is mounted beneath the boat and connects to the engine through the hull.

Our 50 Gal. fuel tank is mounted beneath the cockpit on Starboard side and the fuel line runs the distance through the galley bulkhead.

The engine is almost silent, and purrs along at about 5-7 knots (depending on sea and wind conditions) at 1800 rpms and averages about 5 miles per gallon.

Hope this give a little

[Buzzman]

Just for a laugh - the very first multihull to circumnavigate, David Lewis' Rehu Moana in 1963 - used a single-cylinder 4HP British Seagull Long Shaft 102 Series motor as it's auxiliary.

No reverse - forward only (direct drive) and wouldn't pull the skin off a rice pudding in a blow - but they managed.

In fact, the Plus models in the Seagull range are specifically designed to move large workboats and small barges, and were used for pushing sections of Bailey bridge around during WWII. High reduction gearbox and 13" prop helped, but still with only a 4HP single-cylinder 2-stroke, with rope pull start.

OK, so you'd struggle to make hull speed, but it would push them against tide, wind and waves, where a standard Seagull wouldn't. Probably 3kts or so - wouldn't want to be in a hurry!

But they ARE light.....

[magentawave]

Wow, 13" props on those little egg beaters! Have you heard about anyone making those kinds of modifications to "normal" outboard motors?

Originally Posted by Buzzman

Just for a laugh - the very first multihull to circumnavigate, David Lewis' Rehu Moana in 1963 - used a single-cylinder 4HP British Seagull Long Shaft 102 Series motor as it's auxiliary.

No reverse - forward only (direct drive) and wouldn't pull the skin off a rice pudding in a blow - but they managed.

In fact, the Plus models in the Seagull range are specifically designed to move large workboats and small barges, and were used for pushing sections of Bailey bridge around during WWII. High reduction gearbox and 13" prop helped, but still with only a 4HP single-cylinder 2-stroke, with rope pull start.

OK, so you'd struggle to make hull speed, but it would push them against tide, wind and waves, where a standard Seagull wouldn't. Probably 3kts or so - wouldn't want to be in a hurry!

But they ARE light.....