Shaft angle for old inboard project

[Luchog]

I'm currently refitting an old 19 feet boat originally designed for a 6 cilinder engine and remote v-drive unit.
I want to install a V8 wich is about 300lbs heavier than the 6cilinder engine, and was told to install the engine on the center of the boat using a direct drive transmision, because of bow raising issues.
For this I must modify shaft angle to fit the center of the boat, therefore the propeller will "kick" more water downside.
I was wondering what effects it could have on overall performance/navigation.

Here is a pic of two boats, the one on top is just like mine with a Remote V-drive installed, watch the narrow shaft angle.
The one below is a different hull that has a direct drive unit and wider shaft angle like I would install.
Any advise or comments are most appreciated
Thanks

[woodboat]

The struts come in standard sizes. http://www.glen-l.com/inboard-hdw/struts.html#0127
I would mark where you want to mount the engine then determine your approximate angle. I would however mount the strut then insert the shaft to determine the actual spot to cut the hull.
I prefer Vdrives and weight in the stern. It is very easy to add trim tabs and push the nose over. It is very difficult to get the bow to raise if you mount the engine too far forward.

[Luchog]

My first worry is not nose diving but general tracking/turning since the boat's gravity centre will be moved forward.
Thus ignore what effect different strut angles may have on navigation and power efficiency

I fear the engine on the stern to be too much weight and start taking water in when power-turning even with trim tabs
This is a project ski/wakeboard boat.

[Jango]

Moving the Cg forward can cause problems especially the faster you go.

Since your boat was probably designed for a Vee Drive and rear engine placement, I would assume the bottoms widest point is at the Transom. Conventional Inline Inboards are normally widest near the Motor or Cg (further forward)
.
The combination of increased shaft angle and forward Cg can cause the Boat to bounce especially with increased power. The increased angle provides more Lift BEHIND the Motor tending to lift the back of the boat out of the water.

I would, as a previous Poster suggested, Stay with the rear Engine Vee Drive. Some of the 300 lb will move forward since a V8 is shorter than a straight 6. Shouldn't be a problem in a 19' Boat

[Luchog]

Jango you're right, the bottoms widest point is at the transom. how does it affect??
Wider strut angle/lift behind wouldnt prevent the bouncing??
I was told someone installed a 5.7lts (as i want) in V-drive config. on one of this boats and the bouncing was awful.
Thanks for the imput so far

[Jango]

Luchog,
To provide proper balance, Boat bottom design takes into consideration weight distribution. Normally, bottoms are widest at the transom IF the motor is located there. The wider the bottom (more surface area), the more LIFT.

At higher speeds, If you move the motor (center of gravity) forward, the REAR of the boat will want to LIFT out of the water causing a bounce. Further adding to this problem is the increased shaft angle necessary with an in-line drive.

Wide bottom at the rear, together with moving the motor forward (CG) and shaft angle will also tend to make the Bow "Plow."

Higher speed Ski and Off shore boats locate their motors Aft.

[woodboat]

Well if you use the Vdrive and decrease the angle it will move the engine and transmission forward to compensate without the huge move necessary with a change from V to straight.
Here is a straight inboard hull http://www.glen-l.com/designs/inboard/audeen.html notice the pinch and smaller transom?
Here is a boat for a Vdrive http://www.glen-l.com/designs/inboard/missile.html
See the wider transom?

[Luchog]

All of this is really helpful, keep it coming please.
If I add a fixed position flap on the centre of the transom, how long should it be and in wich angle?? I was thinking about the same as the transom's botton as a continuation of the hull.
Would an extra feet help bow rising issues??

[gonzo]

What engines are you swapping? 300lbs seems like a lot. Also, if you are taking out a VeeDrive, the difference shouldn't be so much.

[Luchog]

The boat was originally designed with a 6 inline 3.6lts, 133 or 166hp in mind.
A 4.3 V8 190hp was available at that time (1974), but it wasnt worth for the weight/power relation.
I want to install a 5.7Gm Crusader in it, 270hp.

[gonzo]

If this is a new engine, the added weight, if any, will be minimal. There may be more than one problem. First, is the boat capable of handling the extra power? Second, will changing the weight distribution affect the ride so bad that it will be worse than before? If it can handle the extra power, keeping the vee-drive would be the best option. The length of the engines is about the same. The mounts are different though.

[Luchog]

The engine I want to install is 1979, so I guees it would not qualify as "new".
My worries are bouncing and turning

Jango mentioned stern lifting/bouncing at higher speeds,
This boat will be used for wakeboarding mostly, so I doubt it will ever reach speeds greater than 30-35 milles, so should I still worry??

[gonzo]

Do you still have the vee-drive. That would be the ideal thing, to keep the engine in the original location. So, do you ski in the Parana River?

[Luchog]

I have just bought a 1:1 velvet Drive and I'm now looking for a 1.5 reduction Remote V-drive unit, there is a national brand that runs up to 300hp. It suits my application well.
Yes, I wakeboard in the Parana River, have you ever been here?
btw, I've checked your site, I wish I could get my hands on some of that stuff you work with.

[cyclops]

Why not got to a commerical meat place that has a scale you could use to weigh the 6 cyl. motor in the boat. Just lift it and let it down . You then have the weight. 5.7L weights are known. Then you know if there is little difference.
Keep the transmission and V drive design if you can afford it. Struts can be cut and rewelded or brased to new shaft angles and then plated new.

[gonzo]

I grew up in Montevideo and did a fair amount of cruising in the Uruguay and Parana.

[Luchog]

I have talked to many people on this topic and I'm handling the possibility of doing a rear engine install with a V-drive unit to avoid cardanic transmission and possible issues there.
Since this will require a wider shaft angle it will help lift the stern to handle engine/transmission weight (800lbs aprox).
I'm looking for a Velvet V-drive 71c, but I can get a good deal on a new Paragon V-drive, any suggestions?

[gonzo]

As long as it is rated for the HP there is no major difference.

[dsharp]

Before you buy the 1.5 Paragon v-drive you need to make sure you can get the bigger prop under the boat unless you're planning on changing the strut. If you decide to go straight inboard- engine placement is often dictated by the depth of the oil pan and bellhousing with respect to the crankshaft centerline. You should be able to get the dimensions from the manufacturer. They're all about the same for the small block chevy's. You can always move your fuel tank or have a tank built to mount across the stern up against the transom if you're worried about being bow heavy. I don't remember the weight on the paragon v-drives but they are heavy as hell. I personally don't care for v-drives. As a mechanic it's hell to re-pack and check the stuffing box. I like to keep my eye on the stuffing box. If you're going to leave the boat on a trailer it won't be that big of a deal though. I've seen my dad do this type of conversion about 10 times. He would lay 2 sheets of plywood down in the shop and draw out the bottom of the boat to figure out the struts, shaftlog placement and dimensions. I should have paid more attention.

[Luchog]

It has been a tough choice, but I have decided to do a direct drive install, wich is easier and cheaper, next month we'll start re-doing the stringers, then we'll place the engine and calculate space for the propeller since I have a 1:1 Velvet Drive, wich I might change to 1:1.23 or 1:1.5 but not sure about this yet.
Fuel thank would be located on the stern against the transom 150lts aprox, and batteries somewhere in the bilge to compesate some weight where needed
this boat is meant to move some weight since this is a wakeboard boat project.
any comments are appreciated

[The Island Man]

Hi
I'm just wondering if you can turn the motor one revolution and the prop two revolutions is that what you mean when you say 1: 1:23 is that like 1 & 1/4 revolutions ? When I heard like a 1.5 to 1 or 2.5 to 1 I always thought the motor was turning more that the prop ? I never heard of it in the reverse ?

[Luchog]

Well, this project has been dead for months now, I've been to busy with work and getting the money needed for the overhaul process.
I still have the Velvet 1:1, I have a buyer for it and my idea was to sell it and get a PCM 1.23:1 8º drive.

Now I have found out about Walter direct-mounted V-drives, and was wondering if it might not be better to keep the Borgwarner Tranny and add it a Walter V-drive, but I can't find any princing for them. Does anyone know where can I get pricing for them?