converting 34ft twin inboards to outboards

Your best bet for hanging those engines would be a Porta Bracket as they are designed to vertically lift engines clean up out of the water without tilting (if you get the long one). They will easily handle 2 engines. I would put on a pair of 150 Suzuki 4 strokes. They have a low (2.5:1) gear ratio and swing a big blade 16" dia. prop. With about a 15" pitch your boat would likely plane nicely and the weight involved would help maintain the proper hull attitude underway and at rest. Your transom is not likely cored (and rotten) so it would be pretty easy to beef up. Sounds like a good project.

 

"don't have to travel far to fish or dive, so I don't need a fast boat, and I don't want to spend a lot of money on engines. The new 4 stroke outboards also have less stinky exhaust."
Well, you are researching things, that's good. BUT here is your oxymoron.
You will find that OBs are MORE expensive overall.
By the time you buy them, the jackplates, the trim tabs AND all the controls that make everything work.... kaching, kaching,$$$$.
Find all this & p: rice them first. You will see used diesel (what you really need) is easier, cheaper to find. Is cheaper, easier to repair and is cheaper to operate. OBs are high maintaince women!
In stall just a single engibe inboard. A Detroit D is a good choise, but any other is good.
As far as the shallow water issue, start researching surface drives. There are several, the ones from Indonesia are reasonably priced. 2 OBs won't save you money, NOT unless the're junk and you are willing to have 'issues' every time you turn around.

 

Surface drives are generally a complete waste of time in a boat of this sort. They are (generally) optimised to run at speeds in excess of 30 knots, and don't usually come into their own until above 40. True, there are some interesting developments on slower speed surface drives just coming to the for now, but they are usually intended for much bigger craft and would make the cost of an outboard seem like a joke!
The twin 150's are similarly a case of overkill. Without knowing a great deal about the boat, I'd say that they would probably not have enough power to get it on the plane, or just barely so. Further, this is a project that is supposed to be providing a cheap to build and economical to run platform. One, or two for redundancy's sake, small outboards would seem the simplest and probably the best to me.
Though, I still have to say that a planing hull doesn't make the best displacement boat, for all the reasons I've previously outlined

 

I agree that it would be a lousy displacement boat, that's why I suggest enough power to make it do what it is designed to do. The weight distribution problem would also be far less given 1000 lbs of engines way out back on a bracket. Additionally, the original poster has expressed the desire to also go well offshore (Bahamas, Cuba). Doing so in that hull with a pair of 40hp outboards would be folly IMO to say nothing about a total lack of market should he ever decide to sell it. The original post indicated a willingness to purchase a pair of 150's. They are 11k USD ea plus about 6k USD to rig them on a bracket, controls, gauges, etc. If that is within the budget then I submit its the best way to get the most use out of this boat.

 

Yes - pottering across the bay is one thing. Venturing offshore, quite another. And as you say, resale value would probably be zilcl as a displacement boat

 

Hmmm... I don't want to have a boat with no resale value, and I understand that I can't make a decent displacement boat out of it. If I were to put a pair of 150hp outboards on it, it still wouldn't plane, I don't think. The factory put 260hp (350 cu in. displacement)gas inboards in the boat - and some people replaced them with 300 hp (454 cu in displacement) gas inboards and said it made a great difference - much better boat. So I'm assuming that 2 x 260hp inboard power just gets the boat on plane.

So maybe I should think about putting inboard diesels in the boat. I'd need V drives - I have two - not a pair - Walter Manufacturing - but they are the wrong style for the boat. So I need to find engines, transmissions, Vdrives, put new shafts and struts in. I can do all this work myself, but I'd really like to not put more than about $25k more into the boat for all of this. And I'd like to have reliability (don't want some hi time engines that may need major overhauls, or break down at sea). I figured with outboards, I could buy new engines and run without much maintenance for five years.

Or maybe put two smaller diesels in.... can't afford 2 x 300hp diesels though...

 

I finally got some photos of the 34C Silverton posted to a website where anyone who's interested can view them.
Check out http://kkropf.photosite.com/

It's in need of cleanup, but the hull is solid - I replaced the wood in the stringers even though Silverton factory said the wood is not necessary for structural strength. The boat was very solid when we picked it up with a crane (2 times)- the local crane operators both said that it seemed like a very strong hull - some boats twist and bend when picked up. Anyhow, I'd like to make this boat move in the water economically, as it is the interior layout that I like.

 

Your problem seems to be 3 things, expence and space to get 2 diesels in there and your draft requirments. Personally I think that 2 outboards will be swamped,-- then your in trouble.

I would spend a serious ammount of time trying to find a used pair of jets with motors that will fit in your space and are from a similar vessel. In comparison to refitting v drives of another flavour this would be reasonably straight forward. It would certainly give you what you want relability, shallow draft, and meet your space requirments and costs( possibly)

Once youve bought a a pair of jets and motors thats it,-- nothing else to buy.

 

mmmm - jets would be a bit of a gamble, I think. True, you'd get the shallow draft, but the boat may be a complete dog at slower planing speeds. Having said that, I have little experience with them, so Jack may well be right...
Swamping outboards can easily be overcome by adding a 'snorkel' so that they draw their intake air from inside the boat.

 

I just cant immagine any thing worse than 2 huge outboards on the back of a cruiser. I dont think that air intake is much of the problem, its more if the engines werent running, once the engine had a bit of water it is done ,-- I mean you cant work on it its too far down. plus being swamped every 10 seconds or the like. If you had to stop in bad seas for whatever i think your main concern would be the engines.
The engines would rot away in 6 months.

The proper way to do this is put back in what came out.

 

Sorry Jack - I don't quite understand where you're coming from. Most bigger o/b's these days have their cowling sealed - with the exception of the air intake. Water shouldn't get inside. There are any number of 'big' boats designed to take outboards - their motors don't simply fall apart....
Having said that, I would tend to agree with you. In this case, if the cheap little displacement bay-cruiser concept is out, then I'd opt for putting in a pair of inboards. Problem is the overall budget here is so limited - and there's no point spending a fortune on this boat: it'd be money down the drain...

 

Well lets be honest - it'll be money down the drain no matter what Keith decides to do as this hull is getting close to obscurity and little value unless it is a mint one owner with original type power. This in spite of the fact that it is a sound, strong hull. I would opt for the outboards for several reasons, not the least of which they are easily transferred to another boat 2-3 years from now should another hull strike his fancy (or reality sets in).

 

Hmmmm....... that is a good point that outboards would be easy to remove and put on another boat, or sell, if this project would fail. An inboard installation will require transmissions, vdrives, new shafts, struts and rudders which would not be easily reused or would bring only a fraction of what I'd have to pay for them. So I'll put another mark in the "go outboards" column.

So, if I put a pair of 70 -150 hp outboards on the boat, I could probably run them just above idle and do 6 knots. If the seas got rough, I could run them harder ... would the boat be able to handle rough weather? Would I need more power for rough seas? I've been in 10-12 foot seas before, but not in an underpowered boat. Do I need a lot of power to handle rough seas? Again, if I don't get up on plane, that's ok, as long as I can handle some rough seas.

 

Well after seeing the picture of the boat its not as big as I had thought, I dont know why but I was thinking of some thing bigger. I now completely change my mind and say that a couple of outboards would be ok. I would also say that In my opinion a pair of 150 might get that on the plane but wieght would be critical.

 

A pair of 150's will almost certainly not be big enough if you want to plane.
If not, there's no point in putting on anything bigger than a pair of, say 50hp. A boat like this will need maybe 20 or 30 hp to run at displacement hull speed (about 5 - 6 knots).
Putiing bigger motors on will only ensure that it uses more fuel.